Fixed and extend NL locale + add test for all

[JeroenVdb]

I wanted to use this library for the nl locale, which was added via PR #351. I noticed some parsers where not correct and/or incomplete and missing tests.

Changed/fixed

• Fixed NLMonthNameMiddleEndianParser: "januari 13, 2012" -> "13 januari 2012"

Added:

• Tests for all nl parsers and refiners
• Added NLCasualDateTimeParser for combined words like "morgennamiddag", "vanavond" and "gisterenochtend"
• Added NLCasualYearMonthDayParser for YMD pattern support

[JeroenVdb]

@Pruxis maybe you should also check these changes as you added the original nl implementation.
I think the biggest (breaking) change is the format fix in NLMonthNameMiddleEndianParser.ts - but in my opinion the old format (January 13, 2012) was just wrong.

[JeroenVdb]

Same for @Thymo as you added the implementation in version 1: #324

[wanasit]

Wow! Thanks for the improvement!
Sorry for my slow reply.