safe way to convert strings to regexps (with options)

 Provides String#to_regexp, for example if you want to make regexps out of a
 CSV you just imported.
 .
 Some features:
  - You can also treat strings as literal regexps.
  - If you need case insensitivity and you're using :literal, pass options
    like :ignore_case.
  - You can get the options passed to Regexp.new with #as_regexp.
  - Finally, you can be more lazy using :detect.