Added RAGE::MemFile + other fixes

+ Added RAGE::MemFile which treats a block of memory as a file.
+ Abstracted RAGE::File and RAGE::MemFile to RAGE::BaseFile class
+ Added RAGE::File loading to RAGE::Music, RAGE::Sfx, RAGE::IniFile,
RAGE::Font, RAGE::Bitmap
+ Added license to source files to which it was missing.
+ RAGE::Music and RAGE::Sfx now can load files during initialization
+ Removed loadFlags and loadStretchFlags and made flags as optional
argument of load and loadStretch
Merge branch 'master' of https://github.com/ArekX/RAGE