Refactoring Session #1. This is an incomplete work. It seems like a big refactor & I think it requires approval for the idea before proceeding.
Merge branch 'develop' into feature/issue70

Conflicts:
	src/Humanizer.Tests/DateHumanizeTests.cs
Replaced current static resource keys with new dynamic resource keys & update usages
Removed what remained from DynamicResourceKeys namespace & updated usages & added a missing test case.
Removed redundant tests + minor code cleanup
replaced boolean isFuture flag with a new TimeUnitTense
Refactored IFormatter & DefaultFormatter /w TimeUnit & TimeUnitTense
refactored TimeSpan.Humanize
applied TimeUnit & TimeUnitTense to TimeSpan.Humanize
Merge branch 'issue70'