Schema Interface

[allonhadaya]

• Change Schema.init to take a pymongo collection instance
• Update the docstrings
• Update the README
• Add an example of new behavior to the README

Resolves #14

[utsavtiwary04]

@nimeshkverma - Please have a look. @allonhadaya - Should we give the user an option to use both the old format and the new one ? Using overloaded constructors, like this - http://stackoverflow.com/questions/141545/overloading-init-in-python

[allonhadaya]

@drcricket - That sounds like a good idea. I'll put it together in the next week as I find time. Thanks!