Text: renamed Text::TextRenderer to Text::Renderer.

No redundant naming. Text::Renderer2D and Text::Renderer3D is typedef'd
to old name, the typedefs are deprecated and will be removed in some
future release.
Math: reduce code duplication in Functions.h.
Math: added rounding functions.
Text: added TODO, minor cleanup.
Text: support for aligning rendered text.
Text: no need to have base class constructor public and documented.