Added support for selective packing to gemmsup.

Details:
- Implemented optional packing for A or B (or both) within the sup
  framework (which currently only supports gemm). The request for
  packing either matrix A or matrix B can be made via setting
  environment variables BLIS_PACK_A or BLIS_PACK_B (to any
  non-zero value; if set, zero means "disable packing"). It can also
  be made globally at runtime via bli_pack_set_pack_a() and
  bli_pack_set_pack_b() or with individual rntm_t objects via
  bli_rntm_set_pack_a() and bli_rntm_set_pack_b() if using the expert
  interface of either the BLIS typed or object APIs. (If using the
  BLAS API, environment variables are the only way to communicate the
  packing request.)
- One caveat (for now) with the current implementation of selective
  packing is that any blocksize extension registered in the _cntx_init
  function (such as is currently used by haswell and zen subconfigs)
  will be ignored if the affected matrix is packed. The reason is
  simply that I didn't get around to implementing the necessary logic
  to pack a larger edge-case micropanel, though this is entirely
  possible and should be done in the future.
- Spun off the variant-choosing portion of bli_gemmsup_ref() into
  bli_gemmsup_int(), in bli_l3_sup_int.c.
- Added new files, bli_l3_sup_packm_a.c, bli_l3_sup_packm_b.c, along
  with corresponding headers, in which higher-level packm-related
  functions are defined for use within the sup framework. The actual
  packm variant code resides in bli_l3_sup_packm_var.c.
- Pass the following new parameters into var1n and var2m: packa, packb
  bool_t's, pointer to a rntm_t, pointer to a cntl_t (which is for now
  always NULL), and pointer to a thrinfo_t* (which for nowis the address
  of the global single-threaded packm thread control node).
- Added panel strides ps_a and ps_b to the auxinfo_t structure so that
  the millikernel can query the panel stride of the packed matrix and
  step through it accordingly. If the matrix isn't packed, the panel
  stride of interest for the given millikernel will be set to the
  appropriate value so that the mkernel may step through the unpacked
  matrix as it normally would.
- Modified the rv_6x8m and rv_6x8n millikernels to read the appropriate
  panel strides (ps_a and ps_b, respectively) instead of computing them
  on the fly.
- Spun off the environment variable getting and setting functions into
  a new file, bli_env.c (with a corresponding prototype header). These
  functions are now used by the threading infrastructure (e.g.
  BLIS_NUM_THREADS, BLIS_JC_NT, etc.) as well as the selective packing
  infrastructure (e.g. BLIS_PACK_A, BLIS_PACK_B).
- Added a static initializer for mem_t objects, BLIS_MEM_INITIALIZER.
- Added a static initializer for pblk_t objects, BLIS_PBLK_INITIALIZER,
  for use within the definition of BLIS_MEM_INITIALIZER.
- Moved the global_rntm object to bli_rntm.c and extern it where needed.
  This means that the function bli_thread_init_rntm() was renamed to
  bli_rntm_init_from_global() and relocated accordingly.
- Added a new bli_pack.c function, which serves as the home for
  functions that manage the pack_a and pack_b fields of the global
  rntm_t, including from environment variables, just as we have
  functions to manage the threading fields of the global rntm_t in
  bli_thread.c.
- Reorganized naming for files in frame/thread, which mostly involved
  spinning off the bli_l3_thread_decorator() functions into their own
  files. This change makes more sense when considering the further
  addition of bli_l3_sup_thread_decorator() functions (for now limited
  only to the single-threaded form found in the  _single.c file).
- Explicitly initialize the reference sup handlers in both
  bli_cntx_init_haswell.c and bli_cntx_init_zen.c so that it's more
  obvious how to customize to a different handler, if desired.
- Removed various snippets of disabled code.
- Various comment updates.

frame/thread/bli_thread.h

@@ -48,6 +48,14 @@
 #include "bli_packm_thrinfo.h"
 #include "bli_l3_thrinfo.h"
 
+// Include the level-3 thread decorator and related definitions and prototypes
+// for the conventional code path.
+#include "bli_l3_decor.h"
+
+// Include the level-3 thread decorator and related definitions and prototypes
+// for the sup code path.
+#include "bli_l3_sup_decor.h"
+
 // Initialization-related prototypes.
 void bli_thread_init( void );
 void bli_thread_finalize( void );
@@ -141,37 +149,6 @@ siz_t bli_thread_range_weighted_sub
        dim_t*     restrict j_end_thr
      );
 
-
-
-// Level-3 internal function type
-typedef void (*l3int_t)
-     (
-       obj_t*     alpha,
-       obj_t*     a,
-       obj_t*     b,
-       obj_t*     beta,
-       obj_t*     c,
-       cntx_t*    cntx,
-       rntm_t*    rntm,
-       cntl_t*    cntl,
-       thrinfo_t* thread
-     );
-
-// Level-3 thread decorator prototype
-void bli_l3_thread_decorator
-     (
-       l3int_t func,
-       opid_t  family,
-       obj_t*  alpha,
-       obj_t*  a,
-       obj_t*  b,
-       obj_t*  beta,
-       obj_t*  c,
-       cntx_t* cntx,
-       rntm_t* rntm,
-       cntl_t* cntl
-     );
-
 // -----------------------------------------------------------------------------
 
 // Factorization and partitioning prototypes
@@ -196,9 +173,6 @@ dim_t bli_ipow( dim_t base, dim_t power );
 
 // -----------------------------------------------------------------------------
 
-BLIS_EXPORT_BLIS dim_t bli_thread_get_env( const char* env, dim_t fallback );
-//void  bli_thread_set_env( const char* env, dim_t value );
-
 BLIS_EXPORT_BLIS dim_t bli_thread_get_jc_nt( void );
 BLIS_EXPORT_BLIS dim_t bli_thread_get_pc_nt( void );
 BLIS_EXPORT_BLIS dim_t bli_thread_get_ic_nt( void );
@@ -209,8 +183,6 @@ BLIS_EXPORT_BLIS dim_t bli_thread_get_num_threads( void );
 BLIS_EXPORT_BLIS void  bli_thread_set_ways( dim_t jc, dim_t pc, dim_t ic, dim_t jr, dim_t ir );
 BLIS_EXPORT_BLIS void  bli_thread_set_num_threads( dim_t value );
 
-BLIS_EXPORT_BLIS void  bli_thread_init_rntm( rntm_t* rntm );
-
 void  bli_thread_init_rntm_from_env( rntm_t* rntm );
 
 // -----------------------------------------------------------------------------