Libqb refactor part 2

[mkilgore]

Part 2 of the libqb refactoring, it should be a bit easier to review. The goals on this step:

1. The list and gfs APIs are split into separate files.
   a. For the gfs API, I removed the global variables, replacing them with two accessor functions gfs_get_fileno() and gfs_get_file_struct(). I also removed the gfs_file_win_struct and simply placed the HANDLE in the gfs_file_struct (similar to the fstreams for the stream-based interface).
2. There are a start to changes to address warnings in the C++ (Ex. const char * instead of char *, #defines that already exist)
   a. -Wno-conversion-null is used to suppress the thousands of warnings produced from passing NULL for unused parameters, which leaves us with a very manageable amount and many which look like actual bugs.
3. I removed usage of libqb.h in audio.cpp, which shows some of the benefits of this refactoring.

Fixes: #147
Fixes: #424