Rename CHANGELOG to CHANGELOG.md

[frankmayer]

I propose that we rename the CHANGELOG file to CHANGELOG.md, so that we can take advantage of directly following the issue- and other- links in the CHANGELOG, instead of having to manually look them up.

There's no bad side-effect whatsoever. Text-only viewers can continue to view the md files with a basic text displayer/editor.

[frankmayer]

Here's a demo of how this would be. Easier readable on github, while readable just the same with a text editor. https://github.com/triAGENS/ArangoDB-PHP/blob/devel/CHANGELOG.md

What do you guys think?

[F21]

+1 This is a good idea. Sometimes, I like to read the CHANGELOG and other text files directly on GH. The markdown formatter goes a long way to make things more readable and usable.

[frankmayer]

So, in order to move forward I am tying up some lose ends. I took the lead on this one and removed CHANGELOG in favor of CHANGELOG.md

I hope you're all fine with this, as it's an improvement and has no negative side-effects.