added email
moved StackatoInterface down a level
changed name to StackatoSession
edited example to reflect change in name
reflected changes to StackatoSession
make username and password mandatory
refactoring token manipulation in the client

This allows users to request and set tokens for a
Stackato session if they have the available data.
fleshed out passwordless constructor
remove unneeded self.token_file
added passwordless authentication
refactor store_token to login function
raise instead of passing
change to TOKEN_FILE
change name to Session
bump version