Initial Release of the F´ SystemReference

This is the initial release of the F´ SystemReference. It includes:

1. IMU Gnc Sensor
2. Camera Payload subsystem
3. XBee Com implementation (must be enabled in topology)
4. Documentation and integration guides

What's Changed

• Delivery by @pelmini in #3

Full Changelog: https://github.com/fprime-community/fprime-system-reference/commits/v0.1-initial