This removes the TinyXML source files, removes it from CMakeLists.txt,
removes all the includes, and removes the functions
FILESYSTEM_saveTiXmlDocument() and FILESYSTEM_loadTiXmlDocument() (use
FILESYSTEM_saveTiXml2Document() and FILESYSTEM_loadTiXml2Document()
instead).
Additionally I've cleaned up the tinyxml2.h include in FileSystemUtils.h
so that it doesn't actually include tinyxml2.h unnecessarily, meaning a
change to TinyXML2 shouldn't rebuild all files that include
FileSystemUtils.h.
This uses utfcpp combined with a custom font, in the form of a PNG and text file. By default, the game acts exactly as it did before; custom fonts can be provided by third parties.
