Change-Id: Ieebea089095d9073b3a94932791099f614ce120c

vpx_codec.mk: Select required sources based on CONFIG_{EN,DE}CODERS.
Relocate _dec_init_ver to vpx_decoder.c to match vpx_encoder.

Change-Id: I6a171bc497499040912b2fb17786fba21a8ebc56

The PLANE_{PACKED,Y,U,V,ALPHA} macros should be renamed to be within the
VPX_ namespace.

Fixes #27

This renames the vpx_codec/ directory to vpx/, to allow applications
to more consistently reference these includes with the vpx/ prefix.
This allows the includes to be installed in /usr/local/include/vpx
rather than polluting the system includes directory with an
excessive number of includes.

Change-Id: I7b0652a20543d93f38f421c60b0bbccde4d61b4f