Man pages: Use similar syntax for synopsis as in xz.

The man pages of lzmainfo, xzmore, and xzdec had similar
constructs as the man page of xz had before the commit
eb6ca9854b8eb9fbf72497c1cf608d6b19d2d494. Eric S. Raymond
didn't mention these man pages in his bug report, but
it's nice to be consistent.
3 files changed