Word-wrap README files and rename them .md

The files' contents are the same as before, I've just word-wrapped them to 80 characters, renamed them to README.md and fixed some markdown related formatting issues.

This way, the files are easier to read, and Github will display them properly.

Lines of code that go over 80 chars haven't been wrapped since they wouldn't display properly anymore (and they're likely to be copy-pasted).