ESP8266/FreeRTOS support.

[vifino]

This is far from done.

• Integrate esp-open-rtos in a submakefile, create sledconf example.
  • I've got little clue about how to do that. I've poked the esp-open-rtos issue tracker for help.
• Create an os_freertos for FreeRTOS support.
• Create an out_esp8266_ws2812b module that uses the i2s peripheral to control ws2812b leds.
  • The esp-open-rtos project has an example, very nice!

[vifino]

@orithena When you got the time, this is something you can help with, eventually. No worries about time.
I'll keep working on this every now and then. :)

I based it on FreeRTOS because this helps a lot. It also should be reusable for different targets.

The esp8266 i2s-based ws2812b backend shouldn't be hard, the esp-open-rtos project has an example, too.

The Makefile stuff is complicated, I am honestly not quite sure how to go about it. Maybe I'll poke the esp-open-rtos guys, perhaps they're willing to help. Maybe they have a bare-bones Makefile that just builds the .a files which you'll have to link in?

[vifino]

So, in theory, one only needs to sort out the Makefile business to get a sled port to the ESP8266 under FreeRTOS, outputting pixel data to ws2812b-compatible pixels.

[vifino]

This definitly needs more lovin'..

The work merged on master will require a little rework on this PR, but it's not too bad.

We just need someone to write a Makefile..

[vifino]

This is a really stale PR in a bad state.
Since #87 exists, I'll close this in favor of it.
When it's merged, it'll add a working and fully-featured os_freertos.

Afterwards, I can try redoing the esp8266 support based on that, which should be pretty simple.