Update and rename developer_guide.md to CONTRIBUTE.md

Cleaned up development process.
Wrap file to 80 characters. Updated some information
Updated README.md file
Do not provide third party exe in tools, added script for that
Better script and updated docs

 1. Check your wine installation if it is 32-bit or 64-bit.
 2. Only download mobigen.exe if it doesn't exists in folder.
 3. General cleanups.
Added script to download tab2opf.py
We don't like spaces in filename
Renamed mobi file
Better formatting
Better scripts
Merge pull request #1 from kartikm/master

Update README and CONTRIBUTE files