This patch adds support for building shared libraries when configured
with the --enable-shared switch.

Building DLLs would require more invasive changes to the sample
utilities than I want to make in this patch, since on Windows you can't
use the address of an imported symbol in a static initializer. The best
way to work around this is proably to build the codec interface mapping
table with an init() function, but dll support is of questionable value
anyway, since most windows users will probably use a media framework
lib like webmdshow, which links this library in staticly.

Change-Id: Iafb48900549b0c6b67f4a05d3b790b2643d026f4

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