feat(conventional-changelog): add grunt-conventional-changelog

- automates changelog generation
- simply run [4mRunning "changelog:from_ref" (changelog) task[24m
[33mWarning: Task "changelog:from_ref" failed. Use --force to continue.[39m

[31mAborted due to warnings.[39m
Merge pull request #38 from PascalPrecht/conventional-changelog

Conventional changelog