Fix project layout

You you can do installations like (replace username):
    
    pip install https://github.com/ionelmc/mongotools/archive/master.zip
    
    pip insall git+git@github.com:ionelmc/mongotools.git

Also, the dependencies must be put in setup.py, not some non-standard requirements file.

These one more thing I'd like to fix - the pymongo dependency should allow for older versions if possible. I've tested this with pymongo 1.11 and it work but I don't have a large db. Are there any issues with old versions?