* Remove a couple TODO messages as they have already been done.
* Add check for parent directory to stop warning about there being no parent scope if building vgmstream directly.
* Remove the options for FDK-AAC and QAAC.
* Fix a few uses of CMAKE_CURRENT_SOURCE_DIR to use VGM_SOURCE_DIR (for consistency sake).
* Fix a few uses of CMAKE_BINARY_DIR to use VGM_BINARY_DIR.
* Add some conditionals for the install paths so they don't show if you aren't building something.
Also had to fix a few of the audacious files to get them to compile, mainly not using NULL in the input plugin constructor and casting the STREAMFILE functions (maybe some *nix compilers would've accepted those, but FreeBSD 12's Clang did not)
