Redesign glottal-stop characters

Redesign glottal-stop characters

Bedstead's various glottal-stop characters were originally based on
its question mark, because that character looks a bit like a question
mark without a dot.  However, while adding a Character Variant feature
for question marks I noticed that the glottal stop and question mark
in the Unicode code charts didn't match, which was why I left the
glottal stop out of that feature.

I've now also looked at the official IPA charts from the International
Phonetic Association, and it's clear that the glottal stop does not in
general match the question mark.  In particular, the join between the
rounded section and the stem is often smooth in a question mark but is
always a right angle in the glottal stop.  I've thus re-designed
Bedstead's glyphs to follow this pattern.  I've also shortened the
crossbar on the glottal stop derivatives that have them, since that
seems to better match DejaVu Sans, which is the sans-serif font
preferred by the IPA.