Function parse 

pub fn parse(spec: &str) -> Result<Source, Fail>

Parse a source spec.

file:///abs/path                      a directory on this box
rsync://[user@]host[:port]:/abs/path  a working tree over ssh
git+https://host/owner/repo#<ref>     a pinned checkout
git+ssh://git@host/owner/repo#<ref>
git+file:///abs/repo#<ref>            a local repository or mirror

The scheme names the TOOL rather than a wire protocol (rsync:// the protocol is the port-873 daemon, which is not what this means), the same convention data_source: already uses for sshfs://.