Force checkout from the top-level directory

The paths listed by `git ls-crypt` are relative to the top-level
directory, so when we perform a forced checkout of files using that
command as the source of our paths, we need to ensure we run git from
the proper location. This prevents pathspec errors and resolves #9.
Ensure touching files works outside of the top-level directory

Related to #9, this fixes up some other uses where the paths used by
certain commands are not relative to the current directory. This would
cause strange bugs when running certain transcrypt commands from
somewhere besides the top-level directory.
Add flag to list all transparently encrypted files

This is a convenience method if the user is unaware of the
`git ls-crypt` alias, but it also works on a repository that has been
cloned but not configured yet (which is a situation when the alias would
not yet exist). Part of the request in #5.
Add flag to show the raw git file object

This is a convenience method if the user is unaware of the `git show ...`
syntax, but it also works when given a path relative to the user's current
directory.

Resolves #5
Fix some minor comment typos
Bump version up to 0.9.6