Changed semantics of blocksize extensions.

Details:
- Changed semantics of cache and register blocksize extensions so that
  the extended values are tracked, rather than just the marginal
  extensions.
- BLIS_EXTEND_[MKN]C_? has been renamed BLIS_MAXIMUM_[MKN]C_?.
- BLIS_EXTEND_[MKN]R_? has been renamed BLIS_PACKDIM_[MKN]R_?.
- bli_blksz_ext_*() APIs have been renamed to bli_blksz_max_*(). Note
  that these "max" query routines grab the maximum value for cache
  blocksizes and the packdim value for register blocksizes.
- bli_info_*() API has been updated accordingly.
- All configurations have been updated accordingly.