version-sync-0.6.0

You can use assert_contains_regex! to grep files for the current version number. The search is done with a regular expression where {version} is replaced with the current version number.

Git dependencies are now always accepted, which means that blocks like

```toml
[dependencies]
your_crate = { git = "..." }
```

will work without you having to add no_sync.

Issues closed:

• #17: Allow to check non-markdown sources.
• #39: Version 0.5 requires Rust version 1.21.0.
• #42: Handle Git dependencies.