Fixed issue #4

Produced confusing message if the .FNT file could not be found, now
produces both a Corona warning and also a FontManager warning, both
with the same thing.
Partial fix to issue 5.

Now copes with imageSuffixes with no font file by checking that it
exists. Lots of warnings though.
Closed issue #3

Bounding box was the wrong size when a font was first created. Fixed
(see github). Probably only a problem for the bounding box, as any
subsequent format at all would fix it.