Update setup_raspberry_pi.md

Update setup_raspberry_pi.md

Update images.

Update stores.md

Update about.md

Update simulator.md

Update setup_raspberry_pi.md

Fixed some typos in build_hardware.md

Fixes #493

added link for finding WiFi configuration file "country" codes.

Replace hand drawn image with a render.
Use lowercase extensions for images.

Add URL to rosbags.

Fix typos.

* ensure docs guide how to handle SD card in a safe way
* make formatting more consistent
* ensure headers about optional steps are easier to spot
* add more details about setting up hostname and discovering IP of the device
* minor fixes

Update setup_mac.md

Update setup_ubuntu.md

Update setup_windows.md

Clarification on what hardware tensorflow-gpu operates

Clarification on when to install tensorflow-gpu

Clarification on when to install tensorflow-gpu

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