Added initial support for imaginary stride.

Details:
- Added an imaginary stride field ("is") to obj_t.
- Renamed bli_obj_set_incs() macro to bli_obj_set_strides().
- Defined bli_obj_imag_stride() and bli_obj_set_imag_stride() and
  added invocations in key locations.
- Added some basic error-checking related to imaginary stride.
- For now, imaginary stride will not be exposed into the most-used
  BLIS APIs such as bli_obj_create(), and certainly not the
  computational APIs such as bli_dgemm().

frame/include/bli_obj_macro_defs.h

@@ -602,6 +602,10 @@ bli_obj_width_stored( obj )
 \
 	((obj).cs)
 
+#define bli_obj_imag_stride( obj ) \
+\
+	((obj).is)
+
 #define bli_obj_row_stride_mag( obj ) \
 \
 	( bli_abs( bli_obj_row_stride( obj ) ) )
@@ -610,6 +614,10 @@ bli_obj_width_stored( obj )
 \
 	( bli_abs( bli_obj_col_stride( obj ) ) )
 
+#define bli_obj_imag_stride_mag( obj ) \
+\
+	( bli_abs( bli_obj_imag_stride( obj ) ) )
+
 //
 // NOTE: The following two macros differ from their non-obj counterparts
 // in that they do not identify m x 1 and 1 x n objects as row-stored and
@@ -641,12 +649,17 @@ bli_obj_width_stored( obj )
 
 // Stride/increment modification
 
-#define bli_obj_set_incs( row_stride, col_stride, obj ) \
+#define bli_obj_set_strides( row_stride, col_stride, obj ) \
 { \
 	(obj).rs = row_stride; \
 	(obj).cs = col_stride; \
 }
 
+#define bli_obj_set_imag_stride( imag_stride, obj ) \
+{ \
+	(obj).is = imag_stride; \
+}
+
 
 // Offset query
 
@@ -998,7 +1011,7 @@ bli_obj_width_stored( obj )
 		doff_t diag_off = bli_obj_diag_offset( obj ); \
 \
 		bli_obj_set_dims( n, m, obj ); \
-		bli_obj_set_incs( cs, rs, obj ); \
+		bli_obj_set_strides( cs, rs, obj ); \
 		bli_obj_set_offs( offn, offm, obj ); \
 		bli_obj_set_diag_offset( -diag_off, obj ); \
 \

frame/include/bli_type_defs.h

@@ -581,6 +581,7 @@ typedef struct obj_s
 	void*         buffer;
 	inc_t         rs;
 	inc_t         cs;
+	inc_t         is;
 
 	// Bufferless scalar storage
 	atom_t        scalar;
@@ -615,6 +616,7 @@ typedef struct obj_s
 	(b).buffer    = (a).buffer; \
 	(b).rs        = (a).rs; \
 	(b).cs        = (a).cs; \
+	(b).is        = (a).is; \
 \
 	(b).scalar    = (a).scalar; \
 \
@@ -657,6 +659,7 @@ typedef struct obj_s
 	(b).buffer    = (a).buffer; \
 	(b).rs        = (a).rs; \
 	(b).cs        = (a).cs; \
+	(b).is        = (a).is; \
 \
 	(b).scalar    = (a).scalar; \
 \