Readable Readme for Androguard

Guys, I wanted to cleanup the readme.txt to a clear Markdown format of the readme. Please don't accept the pull request yet. Some more stuffs needs to be done to make it into Androguard.

- [x] Change the Readme to Markdown
- [ ] Create a separate branch for Wiki
- [ ] Import all the Wiki documents from Google Code to Github.
- [ ] Format them all in Markdown
- [ ] Make the Wiki linkable within each other

If the changes are agreeable, please confirm so that I can send you a more completed pull request.