Change-Id: Ib8f8a66c9fd31e508cdc9caa662192f38433aa3d

Change-Id: Ic084c475844b24092a433ab88138cf58af3abbe4

This commit fixes up shared lib builds on linux.

Change-Id: Ib109dc5a226dc5d7874d2e5b333466cbfd4f4661

Change-Id: I74e50b4dfbe73eb98e1dce1695a9973f637220c0

Having these symbols be available as functions rather than data is
occasionally more convenient. Implemented this way rather than a
get-codec-by-id style to avoid creating a link-time dependency
between the encoder and the decoder.

Fixes issue #169

Change-Id: I319f281277033a5e7e3ee3b092b9a87cce2f463d

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