Changes on send and reception FACe

[nvillarroya]

Breaks Compatibilities:

send method changes.

• Previous behavior has respected in a new function send_by_filename who has the same parameters.
• New behavior
  • invoice_filename: Filename of the invoice
  • invoice_content: b64encoded content of the file who want to send
  • attachments: Same as previous behavior

Return values

• By Default return values are directly from response and not return specific objects.
• Compatibility with previous behavior is so easy. Only need to pass a new parameter on init on kwargs parameters with result_obj=True

   ...
  face = FACe(
         environment=self.environment,
         certificate=self.certificate,
         email=self.email, 
         result_obj=True
     )