goat.1: Document `goat libgoat`

Makefile: Use libgoat subcommand in postinstall message

Add some more cd(1) tests

Add Kyua tests

Make it possible to use "cd -" when using goat alias

Previously, we would call cd(1) on $1 twice, thus loosing the
possibility of going back to the previous directory with "cd -".

Set VERSION dynamically

Chase s/LIBDIR/SHAREDIR/

Improve the short description of goat

Tag 3.0.0

Tag 2.7.0