Make adding text to the document easier

Make adding text to the document easier

tl;dr Use Document::AddText() to put text in places
	Pass the font file in the Document constructor or call Document::SetFont() to change fonts

ts;iwtrm I am not freeing the font data buffer because I strongly suspect we will want to keep it.

You might be able to have arbitrary precision text only documents really easily if you
just re-add the glyphs at a new scale. That might be better than reparenting each individual bezier.

We could add a Document::Finalize() to free memory like the font data
which is used in creating the document but not needed afterwards.

But I want to be able to interactively add text anyway, so there doesn't seem
to be much point at the moment.