Add delete_regex

[jyaworski]

To maintain backwards compatibility, add a third parameter to the delete
function to specify what type the second should be interpreted as. This
is needed for cases where the regex matcher is overzealous.

This was uncovered while testing this against @smoeding's sendmail module as seen here:

smoeding/puppet-sendmail#8

[smoeding]

Either that or introduce a new function delete_regex to clearly indicate a new functionality.

Trying to add the regex functionality to the delete function without giving the user control where the parameter should be used as literal or as regex is a disaster waiting to happen. Just think of all the characters (like '.', '*' or '?') that have a special meaning when used in a regex.

[hunner]

Yeah, I think delete_regex would make more sense from a UX perspective :)

[jyaworski]

@hunner done.