Updated configure.ac to use PKG_CHECK_MODULES.

Also added debug build mode.
Initial working mingw32
Reverted the to_string changes
Fixed string -> to_string typo
Removed unnecessary headers from BaseSurface
Added .o to gitignore
Completed the switch to pkg-config checks.
Updated version number to 0.5.4
Set the correct libtool interface number
Updated docs for 0.5.3