Details:
- Added a new set of reference gemm, gemmtrsm, and trsm micro-kernels that
contain explicit loops over MR and NR, thus allowing them to be used
unmodified by developers who want to build a reference library with
custom register blocksizes.
- Changed config/reference/bli_kernel.h to use above ukernels by default.
- Changed interfaces of new and existing gemm, gemmtrsm, and trsm micro-kernels
to use 'restrict' keyword.
- Added -funroll-loops option to config/reference/make_defs.mk.
- Updated comments in bli_kernel.h describing constraints on register and
cache blocksizes.
- Updated _adds_mxn.h, _copys_mxn.h, and _xpbys_mxn.h macros files so that
single-char macros are also defined.