Implement accurate moment.duration({from, to})
Better bubbling of days to years in duration
Use duration object in relativeTime
internal relativeTime now accepts only duration object
Fix bugs in humanize and asYears
Fix moment tests
Fix language tests
Fix korean test label
Merge pull request #1642 from ichernev/fix-humanize

Fix humanize

@changelog
@section bugfix
@description use duration object for relative duration strings
@breaking relativeTimeThreshold keys are now changed to 's', 'm', 'h', 'd' and 'M'. Also the actual thresholds for changed (46 days is now 1 month, not 2).