Improve changelog. Use markdown etc.

1. Use cute human dates (December 13, 2012 instead of 2012.12.13)
2. Add links to GitHub issues for stuff like #1150 and links to GitHub commits when clicked on version name.
3. Make module names etc. bold.
4. Wrap versions in headings. It allows to make links to sections (CHANGELOG.md#nodejs-094-december-21-2012)

and some other stuff

Example of section:

# Node.js [0.8.16](https://github.com/joyent/node/commit/1c9c6277d5cfcaaac8569c0c8f7daa64292048a9) (December 13, 2012)
* **npm:** Upgrade to 1.1.69
* **fs:** fix WriteStream/ReadStream fd leaks (Ben Noordhuis)
* **crypto:** fix leak in GetPeerCertificate (Fedor Indutny)
* **buffer:** Don't double-negate numeric buffer arg (Trevor Norris)
* **net:** More accurate IP address validation and IPv6 dotted notation. (Joshua Erickson)