* Migrate action|keyboard|keycode|eeconfig from tmk_core -> quantum

This commits add the SH_OS keycode, which works similarly to one shot
layers:
* while pressed, the keyboard is swapped
* if no keys were pressed while it was pressed, the next key press is
swapped

SH_OS also supports chaining with one shot layers:
OSL(x) + SH_OS + key interprets the key press on the oneshot layer.

The ONESHOT_TIMEOUT setting used by one shot keys and layers is also
used by oneshot swap hands. In the above chaining scenario the timeout
of the oneshot layer is reset when swap hands is activated.

Resolves #2682

* Remove ACT_COMMAND

* And from action_t as well

* Extend allowed range of tappable keycodes to include modifiers

* Get rid of the magic numbers altogether

* Remove some more magic numbers

* Extract LM() functionality from ACT_LAYER_TAP

* Use ACTION() macro everywhere

* Generate api docs from source code

* Add a bunch of doxygen comments

* more doxygen comments

* Add the in-progress api docs

* script to generate docs from travis

* Add doc generation to the travis job

* make travis_docs.sh commit the work it does

* make sure the docs script exits cleanly

This is an inelegant hack for #2522 but makes things work. Basically we give `action.c` a chance to handle the hold event early so that we can swap the keyboard for later keys. Later, to allow the hold to happen again quickly we nuke the key record so that tapping is reset. I tried to find a cleaner way, honestly.

* add breathing to bananasplit

* backlight breathing overhaul

* fix the backlight_tick thing.

* fix for vision_division backlight

* fix a few keymaps and probably break breathing for some weirdly set-up boards.

* remove BL_x keycodes because they made unreasonable assumptions

* some fixes for BL keycodes

* integer cie lightness scaling

* use cie lightness for non-breathing backlight and make breathing able to reach true max brightness