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
This doesn't play well with autotools, and the preprocessor magic is
confusing and unhelpful in the vp8-only context.
Change-Id: I2fcb57e6eb7876ecb58509da608dc21f26077ff1