Feature request: literal "search" option

[kylecordes]

This is a very powerful and useful package. However, sometimes it is necessary to search for strings that require unpleasant amounts of escaping to make them valid as a regular expression.

Therefore, a simple feature request:

Offer a command line option --literal or something like that, which makes the search just for the exact literal string provided, not a regular expression.

[Xotic750]

It should be a fairly simple task to add that option, then use RegExp.escape to escape the literal string. I'm willing to take a PR.