Rename `CHANGELOG.md` or make it Markdown

[pmcnr-hx]

Either rename CHANGELOG.md to CHANGELOG.txt or make it proper Markdown, otherwise GitHub renders it nastily. While we're at it, it'll probably make sense to reorder in chronologically inverse order with the most recent entries first.

[theninj4]

Haha, you're absolutely right! Doh.

[pmcnr-hx]

This has been fixed in #98.