V0.4.0 RC1

* complete rewrite and overhaul
* move all docs to doxygen
* all subsystems are now in independent headers
* move gpio to new device driver
* move ADC from mmap to iio
* deprecate rc_initialize(), new functions for handling PID files/signals
* most examples no longer require root
* all examples are dependent on single subsystems for portability
* pwm through driver instead of mmap
* mpu9250 IMU config allows custom gpio pin and address
* mpu9250 DMP tap detection allowed
* mpu9250 dmp mode can now run slower than 200hz
* button interface allows custom buttons
* uart interface allows config on initialization
* add mavlink interface over udp
* add PRU interface for custom PRU binary loading
* split encoder counting on eqep and pru to avoid conflicts
* cpu frequency interface now controls scheduler
* LED interface controls battery LEDs, USR, and WIFI leds
* various renaming and fixes in math lib
* single include for all math sub-libs
* new pthread helpers
* servo interface now has same function to handle one and all channels
* battery monitor has startup and power-change flash patterns
* roboticscape systemd service helps set permissions of device drivers
* project template demonstrates PID file and signal handling
* new rc_test_esc example
* new makefile for examples means all src files can be in same folder
* all makefiles keep src/bin folders separate

Known Bugs:
* MPU accelerometer calibration ignored for now until fully tested
* missing rc_dsm_passthrough until fully tested