Massive renaming. This fixes a mistake made right at the beginning of
the library, and is something I've wanted to fix for the longest
time. Basically, the fileformat is 'ipuz' and the capital 'P'
shouldn't exist.

find ./ -type f -exec sed -i -e 's/IPuz/Ipuz/g' {} \;
find ./ -type f -exec sed -i -e 's/I_TYPE_PUZ/IPUZ_TYPE/g' {} \;

This stops us fighting against glib tooling, too, as it really wants
the function names to be i_puz (and I_TYPE_PUZ).