Like the spec says, if a value for the @include or @exclude rules starts
and ends with a '/' it should be parsed as a regular expression.
Technically a ECMAScript syntax regular expression, but I am not sure of
the differences and I assume they are far fewer than the similarities.
One that I did see mentioned was that javascript RegExp doesn't support
unicode. Although it apparently does support a 'u' flag now.
Note that code will only be ran for QtWebkit and QWebEngine < 5.8
we rely on the builtin support for metadata it QWebEngine for most
things greasemonkey related. Sadly it seems that they missed the regex
requirement too. I've opened a ticket to track that https://bugreports.qt.io/browse/QTBUG-65484
