Support PWMThrottle and PWMSteering as threaded part to improve performance. Minor (most whitespace) code cleanups (pep-8).

Update README.md

Fix image extension, since they are lowercase now.

Travis update

Documentation: Editing myconfig.py without changing directory

The previous page of instructions could mostly be copied and pasted into terminal and would work. This small change allows that to continue for this line.

black - The uncompromising Python code formatter.
https://github.com/psf/black
It requires python 3.6 or newer, though

Update formatting such as:
* missing clickable urls
* wrap in backticks special words (at least most of them)
* fix lists due to missing newlines
* wrap code sections into proper code blocks
* remove some improperly created headers

Rename files to lowercase extensions
Remove +x permissions set on files

Todo - look into legacy.md and extract data from it into another docs.

* Add stages for makrdownlint, yamllint, mkdocs
* Update travis config so that it no longer generates warnings if pasted
  into https://config.travis-ci.com/explore
* Speed up linting phase (skip install)
* Move docs build earlier
* Allow yamllint and makrdownlint to fail

retry of pwm.set_pwm on first exception due to I2C timing errors

add a new joystick class known as RC3ChanJoystickController

add arg for custom figure format (e.g. 'png', 'pdf', 'svg' ...) for train.py

check TensorFlow version before overriding keras session

Small performance improvement and jitter output in ms

Improve performance by replacing division /255 with multiplications and adding some pep-8 formatting. Also fixing jitter output to be in ms

Fix typos in setup_raspberry_pi.md