Merge decoder and encoder libs, and use dynamic linking

[SuperStik]

Significance:

• Consolidates both encoder and decoder libraries into one source.
• Uses dynamic linking, with all the benefits that comes with it

Testing:

• Successful compile
• Encoder and decoder library produced the same output

[SuperStik]

Might be a good idea to keep the static encoder and decoder libraries separate, but I'm not too sure

[Kong32222]

May I ask if the library supports 42

[colisee]

I am also in favor of @SuperStik proposal, for I'd like to switch to libxaac from fdk-aac in the opendigitalradio audio encoder