Update prune docs and a few other things in usage.rst.
Various minor documentation updates: mention sshfs, Linux packages,
minor changes to prose, etc.
Update README.rst.
Merge pull request #32 from jdchristensen/docs2

Docs2: update lots of documentation
Basic repository consistency check functionality.

Still no archive metadata validation or repair functionality.
Removed some dead code.
Fixed repository check progress reporting.
Remove flush=True argument from print() since it is Python3.3+
Only cleanup partial transactions if an existing transaction is found
Add more tests to PatternTestCase.  The first two fail with the
current code.
Fix minor bugs in IncludePattern and ExcludePattern, and speed up
ExcludePattern by storing a compiled regular expression.
Add one more test to PatternTestCase.
Simplify IncludePattern and add a few more tests to PatternTestCase.
Simplify the ExcludePattern logic further, and explain.
Fix a doc typo.
Merge pull request #33 from jdchristensen/exclude

fix include/exclude bugs and add more tests
Repository code cleanup