Let RegexHighlighter highlights unnamed groups instead of only named ones

[IgorBonaP]

Hello!

Thank you for your great package, really neat stuff.

I was fiddling with a custom RegexHighlighter and noticed that it only highlights the patterns enclosed in named groups.
I was wondering if there is interest in allowing regex highlighting of unnamed patterns?
This would be useful if a user wants to match multiple patterns to the same style.
I could not find an example on how to do that in the docs so I worked around this.

This behavior results from the following line on the Text class within text.py:

for name in match.groupdict().keys():

A simple workaround is to check for groupdict() first and in case there is none append only the style preffix to the matched span.

Keep up the good work.

Cheers,
Igor