Physical character simulation - robust movement

[u/JeroenDierckx]

After natural running, now more varied movement on different surfaces.

[u/JeroenDierckx]

After stable and natural running, I started training other parts of the movements I would like in a game:
* stopping and turning around quickly
* facing any direction while moving
* jumping and recovering
* getting up from the ground
* moving on different ground types
* start of a running backflip

Tested two changes to the physics:
* elastic tendons for knees and ankles, really helps with takeoff and landing so I kept it
* multi-joint muscles (hamstrings etc) in the legs but did not improve results so did not keep it (the simpler the better)

I also did a first test with an adult body, starting with the brain of the smaller character. Not playable yet but makes for funny slapstick.

Too much tasks in the base brain has a big toll on training, and since I am just doing this in my free time with my two GPUs at home I am moving to a base brain with specialized sub brains that are activated for certain tasks.

Not really mixture of experts: the specialized networks are activated directly from gamepad buttons now.

Gamepad controls I am settling on for the playable character:
* left stick for movement direction and speed
* right stick for different facing direction than movement direction
* hold A to prepare for one-footed jump, let go to actually jump
* B for the same with two feet
* left trigger for backflip modifier, right trigger for frontflip
* bumper for roll modifier on landing or running
* Y to play dead (disables all muscles)

I did a quick test with a running backflip, but the rest of flips and rolls are not trained yet.