doc/api.html : Fix typos.

Patch-from: Jan Stary <hans@stare.cz>
man/sndfile-(convert|salvage).1 : Typos.

Patch-from: Jan Stary <hans@stare.cz>
man/Makefile.am : Hook up sndfile-salvage.1.

Patch-from: Jan Stary <hans@stare.cz>