support look around for regex pattern matching

[webbdays]

Use fancy_regex crate instead of standard regex crate.

Thank you very much.

[sunshowers]

Thanks for the report! Could you elaborate on your use case? I've used datatest-stable a few times and have never needed anything beyond basic glob-like regexes.

[webbdays]

example
match .md
but not .skip.md

[sunshowers]

Done as part of #43 and released in version 0.2.7. Thanks again!