findkey.py should be able to query by regex

[williballenthin]

The sample findkey.py should be able to query Registry key/value/paths by regular expressions, rather than simple exact text matches. I propose adding an additional flag to the command line, -r that specifies that the query should be interpreted as a regular expression. For instance:

findkey.py -r SYSTEM.hive  "[Bb]eep"

Should have to add an additional import for re.