Add changelog entry for v1.4.0 (uber-go#429)

Add a changelog entry for the 1.4.0 minor release.

Add v1.3.0 to changelog (uber-go#417)

* Add v1.3.0 to changelog

* Reword slightly

Add v1.2.0 to changelog (uber-go#407)

Add v1.1.0 to changelog (uber-go#398)

Really fix README link

Update changelog for RC 3 (uber-go#356)

Update changelog and readme for RC 2 (uber-go#329)

Update changelog for RC1 release

Add RFC3339NanoFormatter and UnixNanoFormatter (uber-go#276)