Formatting fixes for man page

There is no .R; replace badly-nested .RE with .PP;
use hyphens to introduce options rather than en dashes
(addresses samtools/www.htslib.org#5 for tabix man page).
Fix regidx.o dependencies and htslib.mk; alphabetise
Merge man page formatting fixes
Support for Type=Character, in htslib same as Type=String