Hack WS2811 led strip.  Proof-of-concept.
Update the ws2811 led strip code for orientation and battery warning.

When armed the first half of the strip is green the second half is red.
When disarmed the strip is various shades of red.
When the battery is low the strip will flash.
Fix WS2811 RAM usage by using the correct types.
Cleanup WS2811 code and sanitize API.

Removed many magic numbers.
Deduplicated code.
Removed unnecessary local variable usage.

The LED Strip is initialised to WHITE briefly on power up so that it's
possible to visually check that all LEDs are functioning correctly -
white uses each individual RGB diode and draws maximum power.

Introduced an API to allow any code to change any or all LED colors
individually.  This takes a little ram since an additional buffer is
needed - 3 bytes per LED, in addition to the DMA buffer.
Quickly hack up implementation of turn indicators.

With an LED strip length of 10, arrange the leds clockwise from 1 to 10
starting with led 1 at the north west (10:30hrs) with led 5 north east
(01:30hrs), led 6 south east and led 10 south west.

When armed or not, moving the roll stick to the left will make the leds
on the left flash, and same for right and also for pitch forwards and
backwards too.
Update turn indicators and battery led flashing to operate
independently.

Turn indicators now flash faster the more you're turning.
Change LED strip colors based on flight mode.
Change precedence of LED flight mode colors.
Improve cycle times by avoiding an led strip update while one is still
in progress.
Extract STM32F10x specific WS2811 code into separate file, ready for
STM32F30x port.
NAZE - Fix LED0 GPIO selection.
Fix divide by zero error which resulted in way too many LED updates
being sent.

This was the root cause of the loop time increase that was seen.
Remove unnecessary includes.
STM32F30x - Support WS2811 LEDs.
Relocated led strip user code into separate file.

Added documentation.

Added LED_STRIP feature, can only be enabled under certain circumstances
depending on target due to pin/timer mappings - see documentation.
Update developer TODOs.
Merge branch 'ws2811'