The timer was not being initialised correctly, it only worked by
accident due to timer configuration of other timer channels. This
explained why TIM3 didn't work in the mapping exclusion for the CC3D and
why for the LEDs to work correctly TIM2 had to be specified so that TIM3
was actually accidentally initialised still.
This required timer overflow events to be used in the calculation of PPM
channel data.
CC3D tested, other targets may be unstable as a result. Needs further
testing.
Added documentation.
Added LED_STRIP feature, can only be enabled under certain circumstances
depending on target due to pin/timer mappings - see documentation.
