add 'copy' argument to put password into clipboard

Works like 'get', but uses `xsel` to copy the first result to the
X CLIPBOARD selection and produces no output on success.
put version data into separate file

Otherwise using setup.py to install won't work if not all dependencies
are already installed, as the import of yspave.pave relies on them.

Also bumped the version number there to 0.0.8 as in the git tag and the
PKGBUILD.
add xsel dependency to PKGBUILD
Merge branches 'metadata' and 'xsel'