Add automated changelog

[gillchristian]

I gonna quote @ianaya89 ( #47 ) on this

We should consider create a CHANGELOG.md file to include this new stuff.

I think we should automate it. Some options:

• semantic-release. It automates the whole release process, but does not generate the changelog file ~I think~. :grimacing:
• generate-changelog. Generates the changelog file. I think this one is a better fit with our current release process that uses np for the versioning.

[ianaya89]

I like generate-changelog. I think we need to start to be more consistent with commit messages. Anyway I am sure we can manually tweak changelog after being generated.