Added high-level implementations of 4m, 3m.

Details:
- Added "4mh" and "3mh" APIs, which implement the 4m and 3m methods at
  high levels, respectively. APIs for trmm and trsm were NOT added due
  to the fact that these approaches are inherently incompatible with
  implementing 4m or 3m at high levels (because the input right-hand
  side matrix is overwritten).
- Added 4mh, 3mh virtual micro-kernels, and updated the existing 4m and
  3m so that all are stylistically consistent.
- Added new "rih" packing kernels (both low-level and structure-aware)
  to support both 4mh and 3mh.
- Defined new pack_t schemas to support real-only, imaginary-only, and
  real+imaginary packing formats.
- Added various level0 scalar macros to support the rih packm kernels.
- Minor tweaks to trmm macro-kernels to facilitate 4mh and 3mh.
- Added the ability to enable/disable 4mh, 3m, and 3mh, and adjusted
  level-3 front-ends to check enabledness of 3mh, 3m, 4mh, and 4m (in
  that order) and execute the first one that is enabled, or the native
  implementation if none are enabled.
- Added implementation query functions for each level-3 operation so
  that the user can query a string that describes the implementation
  that is currently enabled.
- Updated test suite to output implementation types for reach level-3
  operation, as well as micro-kernel types for each of the five micro-
  kernels.
- Renamed BLIS_ENABLE_?COMPLEX_VIA_4M macros to _ENABLE_VIRTUAL_?COMPLEX.
- Fixed an obscure bug when packing Hermitian matrices (regular packing
  type) whereby the diagonal elements of the packed micro-panels could
  get tainted if the source matrix's imaginary diagonal part contained
  garbage.
Merge branch 'master' of github.com:flame/blis