Beginning to expand support for other currencies and locales

This begins to add support for other currencies and locales while handling other parsing edge cases.

Specific changes are:

• "1,,000" is now correctly recognised as an invalid format, previously it would parse to 100000
• Decimal separators other than . are now supported, though not yet exposed publicly.
• Grouping separators other than , are now supported, though not yet exposed publicly.
• A public interface has been added for Parser.

Next steps:

• Further research onto different money formats beyond what I've already handled.
• Once I'm confident the parser can handle all necessary formats I'll provide a stable public API for parsing money for any currency or locale.

Initial release

Support for efficiently parsing USD values.