Font and text layouting is now abstracted out from its implementation.
Font class is renamed to FreeTypeFont and all the work can be done
through AbstractFont and AbstractLayouter interface.
The coordinate is always 0 and Mesh can be configured to add it
implicitly. The code is now nearly the same for 2D and 3D, will redo it
without templates later.
The library uses FreeType for glyph pre-rendering and basic glyph
geometry and HarfBuzz for text layouting (i.e. ligatures, kerning, ...).
Currently all used glyphs must be prerendered into texture atlas, other
glyphs are simply not rendered (although the layouting code handles them
like if they are there).
Text rendering supports UTF-8, although glyph pre-rendering is currently
ASCII only, as I couldn't find any working implementation of Unicode
STL function in recent GCC versions. Will be fixed later.