xml2kvp: regex on value, copy to target field

[ghukill]

Add ability to copy values that match regex patterns to a new field.

e.g. the values foo123 and bar123 are encountered. If the regex pattern .*123.* is entered with a target field of baz, those values will be copied to baz as well.

Could be similar to field copying, with an optional filter to remove those values from original field.

[ghukill]

Implemented:

In [3]: XML2kvp.xml_to_kvp(XML2kvp.test_xml, copy_value_to_regex={'.*[0-9]+.*':'NUMBERS'}, remove_copied_value=True)
Out[3]: 
{'NUMBERS': ('42', '109', '9393943', '3489234893'),
 'root_beat_@type=3/4': 'waltz',
 'root_beat_@type=4/4': 'four on the floor',
 'root_goober_@scrog=true_@tonk=false_depths_plunder': 'Willy Wonka',
 'root_internet|url_@url=http://example.com': 'see my url',
 'root_nested_attribs_@type=first_another_@type=second': 'paydirt',
 'root_tronic': 'You may disregard',
 'root_tronic_@type=tonguetwister': ('Sally sells seashells by the seashore.',
  'Red leather, yellow leather.')}