Added leftZeroFill to GGGG and gggg formats
Expanded test for iso week formats to include W format
Fixed typo in tests for week year formats
Updated source link
Added 3-digit years to tests for GGGG and gggg formats
Merge pull request #1396 from mdxs/left_zero_fill_gggg

Add leftZeroFill to GGGG and gggg formats

@changelog
@section bugfix
@description Add leftZeroFill(4) to GGGG and gggg formats