v1.2.0

- Feature: added a GPS-enabled packet forwarder, used to timestamp received
packet with a globally-synchronous microsecond-accurate timestamp.
- Feature: GPS packet forwarder sends status report on the uplink, protocol
specification updated accordingly (report include gateway geolocation).
- Feature: packets can be sent without CRC at radio layer.
- Bugfix: no more crash with base64 padded input.
- Bugfix: no more rounding errors on the 'freq' value sent to server.
- A minimum preamble of 6 Lora symbol is enforced for optimum sensitivity.
- Padded Base64 is sent on uplink, downlink accepts padded and unpadded Base64.
- Updated the Parson JSON library to a version that supports comments.
- Added .md (Markdown) extension to readme files for better Github viewing.