It returns all the fonts (possibly more than 1) with a given name. I left the
function gimp_font_get_by_name() as a utility when one don't want to choose (or
is not able anyway, e.g. a script with minimal information), though I wondered
if we should not simplify with a single function (the new one, which is the
correct one now that it is possible to have several fonts with a given name).

It is easy to test with fonts named the same. For instance I could find 2
different fonts, both named 'Holiday'. This call in the Python console returns
both:

> Gimp.fonts_get_by_name('Holiday')

As part of this commit, I also implemented resource arrays (or subtype arrays)
as PDB arguments and return types.