Simple PO file to ruby hash parser

 This is a simple PO file to ruby hash parser, which complies with GNU PO file
 specification. Tested with the msgcat (GNU gettext-tools) 0.18.3 tool.
 .
 The parser is probably as optimized for speed as possible with pure ruby,
 while parsing all different PO types into separate keys. It was written as a
 "core-replacement" for an equivalent parslet PEG parser for arashm/PoParser
 and benchmarked about 500 times faster.