Improve speed of _fixWidth

The benefit of this is fairly noticable on a web page that formats a couple hundred dates. It is logically the same, but instead of string concatentation, it uses arrays and at the end performs a join.
Turn numbers into strings when stringifying the timezone data.
Calculate correct string length while padding new string
Merge pull request #118 from mkadin/numbers_as_strings_in_stringify

Turn numbers into strings when stringifying the timezone data.
Fix copy paste mistakes that made it through tests
Add tests to verify the format trimming and padding work as expected
Only trim years, as trimming others would cause loss of meaning
Merge pull request #117 from beeftornado/fixWidth-perf

Improve speed of _fixWidth