Add missing files

[tlugger]

In the spirit of being meta:

➜  flint git:(master) go run flint.go
[WARNING] CHANGELOG not found
[INFO] Add a changelog to show what's new or improved with each release. http://keepachangelog.com/
[WARNING] CODE_OF_CONDUCT not found
[INFO] Let people know what to expect when they participate in the project

This repo was missing some of the files it was built to check for. I have added a boilerplate code of conduct from Contributor Covenant and a beginning for a changelog.

Additionally, I made the remote project matching case insensitive for filenames as I've seen variations of Changelog, CHANGELOG, and changelog among other files this checks for.

Also closes #48