Rewrites & Updates:

- Abstracted APRS-IS TCP server connect logic out into `APRS.connect()`,
  which must be called before you send or receive from APRS-IS.
- Added support for APRS-IS Send-only on HTTP & UDP, as well as
  send/receive on HTTP.
- Linted, PEP8'd and cleaned up code.
- Updated docs.
- Updated docstrings & Copyrights.