Feature Request [python.nanorc]: add f-string support

[jwest75674]

Newer versions of python have the super awesome format string / f-strings (https://www.python.org/dev/peps/pep-0498/)

However, these don't have syntax highlighting here just yet.
This appears complicated due to f-strings appearing within strings in regard to color, but this would be an awesome funcitonality.

[davidhcefx]

There's a trick that by placing a highlighting rule after another, the text color will be applied by the latest rule. Maybe highlight strings first and then other syntaxes. But then the problem is we need lookahead assertions, which is not available in ERE regex.
Maybe we need to look into how other editor done this.