Fix make install to install man pages #35
Fix make install to install man pages #35

Now installs man pages to INSTALL_PREFIX/share/man/man8/foo.8.gz

Breaking change:
- INSTALL_PREFIX no longer a full path to bin dir; rather, it now
must be a directory containing the bin & share/man directories.

Other improvements:
- make clean handles still-mounted test btrfs filesystems in /tmp
- make distclean cleans up tmp/bats

florianjacob/snazzer,csirac2/snazzer,florianjacob/snazzer,csirac2/snazzer