add link to changelog

[jlgeering]

link will be picked up by hex and added to https://hex.pm/packages/timex next time a version is published

for example see https://hex.pm/packages/quantum

Summary of changes

new "Changelog" link on https://hex.pm/packages/timex to https://github.com/bitwalker/timex/blob/master/CHANGELOG.md

Checklist

• New functions have typespecs, changed functions were updated
• Same for documentation, including moduledocs
• Tests were added or updated to cover changes
• Commits were squashed into a single coherent commit

[coveralls]

Coverage decreased (-0.6%) to 69.269% when pulling 464914f on jlgeering:link-to-changelog into ea3cd35 on bitwalker:master.

[jlgeering]

Coverage decreased => that is unfair :-)

should I write a test that covers mix.exs ?

[bitwalker]

Yeah, coveralls is really dumb about calculating coverage, I probably just need to tweak some configuration to ignore mix.exs