Improve test coverage for TzDatabase
Set noImplicitAny in gulp file
Merge pull request #13 from daanwissing/master

More format implementations
Merge pull request: add DateTime format function.
Adjusted documentation and some function names; exported more utility functions.
Publish version 1.5.0
Publish version 1.5.1: bugfix in method name secondOfDay() and in typings.
Replace timezone id "GMT" (which means "Greenwich Mean Time") with UTC (which means "Coordinate Universal Time") with formatting.

Althought the LDML standard specifies GMT to be used for timezone offsets,
UTC is a better alternative to the old-fashioned GMT.
Add more examples of formatting a DateTime.
Update documentation,