Change released version to 1.4.1

Sadly, I uploaded the wrong file to PyPI for 1.4.0. Once you do this, PyPI
never lets you change the file associated with a given released version. So we
need to use 1.4.1 instead. 😢

Add release date for 1.3.19

Add date for 1.3.18 release

Add date for 1.3.17 release

Date for 1.3.16 release

Add date for 1.3.15 release

Finalize changelog

release.py: push the commits too

Datesamp 1.3.12 release

Merge branch 'master' of github.com:sampsyo/beets