Inefficient regex in extract_full_summary_from_signature

[jiasli]

As pointed out by https://gist.github.com/prodigysml/d07cd482214c80bfb6d3240454d2f679, this regex (introduced by 430c39e) is inefficient:

knack/knack/introspection.py

Line 18 in e0c1411

regex = r'\s*(:param)\s+(.+?)\s*:(.*)'

As shown in https://regex101.com/, a simple :param r requires 1214 steps to fail.

This is because \s+, .+? and \s* all match consecutive spaces, thus can trigger many backtrackings.

A better solution is to replace .+? with \w+ to match the parameter name so that backtrackings can be greatly reduced:

\s*(:param)\s+(\w+)\s*:(.*)