man/sndfile-interleave.1 : Improvements including exit status and examples.

Patch-from: Jan Stary <hans@stare.cz>
man/sndfile-info.1 : Document command line options.

Patch-from: Jan Stary <hans@stare.cz>
man/sndfile-play.1 : Improvements.

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