Add cmake module to find SDL_ttf
Add SDLTTF class for SDL_ttf init/deinit
Add stub for Font class
Add option and check for SDL_ttf support, add ttf files to build
Add ttf-related includes to the main header
Add stub for ttf example
Install library and font necessary for ttf support
Add more possible paths to Vera.ttf
If font is not found, just don't build example instead of failing
Bundle Bitstream Vera font

It's not that large (even smaller than our example .wav file), has
liberal license and saves us from complexity of finding system
font. Later I may consider installing it as a default font to make
ttf features of SDL2pp usable out-of-box without need for extra
fonts.
Fix structure name in documentation
Merge branch 'master' into ttf

Conflicts:
	CMakeLists.txt
	SDL2pp/SDL2pp.hh
Implement basic ttf rendering, use in example
Fix documentation
Add SDL2PP_WITH_TTF knob to Config.hh
Offset by real surface size
Make example more demonstrative
Implement all font rendering functions
Implement whole SDL_ttf
Add two convenience functons for gllyph metrics retrieval