Add documentation, change to named parameters to all functions, update tests and add example code.

Changed all functions to use named parameters to follow the Stripe API.  This will break some existing code that relied on positional parameters.  See the documentation for changes and new examples of calling functions.  One example get_invoice() you now must pass get_invoice(invoice_id => $id) where you previously called get_invoice($id).  I think named parameters allow more flexibility and expressiveness.

Added documentation of each function along with an example call of that function to the POD documentation.  

Described all method's accepted parameters and types.

Changed to using MooseX::Method::Signatures rather than method module to remove some older dependencies and add better type checking to parameters.

Reworked live.t to reflect the API changes.