Update README.md

demo link added
sanity refactor with callbacks
avoid ECMAScript 5 properties for compatibility
pagination for gcontacts
extra info on pagination && timeoutSession

 - pagination moved to an object with extra information
 - removed window._GcontactsTokenTimeout in favour of
   timeoutSession variable inside the library
 - internalRandomCode complex than only numbers avoiding
   errors on square brackets use over jsonp callback
Merge pull request #5 from eventioz/callbacks_and_pagination

Callbacks and pagination
basic documentation for Gcontacts
we take redirect_uri on init if we wish to do so.
fixing interation over data & %s/options/pagination/g
we rename the exported function for better representation
some clarifications over redirect_uri
we change login event for cb function