Gprs reporting

[amcgee]

Implement GPRS reporting and refactor the GSM APIs

To be reviewed and squashed before merging

[amcgee]

(AppVeyor hasn't been fully set up yet, please ignore)

[amcgee]

This should be ready to go now. I'll merge once the CI finishes. The final squashed commit reads:

---

Refactor the internal GSM module api for serial communication with the SIM900, and implement GPRS reporting.

Specifically:

• Implement basic multi-server report failover
• Update GSM module code to work better with the new hardware
• Update the xc8 1.33 download hash.
• Remove non-working intelhex test.
• Remove the 'asm' compiler optimization for gsm_module - it was causing weird logic errors
• Implement bimodal comm streaming (sms and GPRS/http)
• Change the comm stream api to accept a destination separately (using a new set_comm_destination RPC) and accept a length when opening a stream.
• Don't retry reports that weren't initiated by the controller.

[timburke]

Merging this so that I can use it. Also, I added two filter capacitors to the old design and am not able to trigger the voltage reset bug on sending a text!