Add 2.1.0 changelog notes

Add a few more release notes

Add version 1.5.0 changelog notes

Cut version 1.4.0

Bump CHANGELOG

Fixes #440, version 1.3.2

Add changelog for 1.3.1

Merge pull request #435 from tripit/dev

Thanks @lord and everyone contributing! Slate v1.3 ftw!

Merge pull request #292 from tripit/dev

Slate 1.2.1
@lord my fault, I seemed to have totally missed the emails sent!

Merge pull request #281 from tripit/dev

Slate v1.2
holy moly that's a lot of changes! 👍