… section. Added a tour of the code. Fixed a grammar error.

…Batavia types.

Conflicts:
	docs/how-to/contribute-docs.rst
	docs/how-to/index.rst

Decided to resolve the `docs/how-to/index.rst` conflict as not including the titles (i.e. follow the Don't Repeat Yourself or DRY principle). A rendered example can be seen at:
https://batavia.readthedocs.io/en/latest/how-to/

This builds on #816 though as noted there it leaves the docs somewhat repetitive and so more completely merging with #823 seems appropriate.

#819 (comment)

I can see the pythonanywhere.com is at 3.7.0, though CPython is considered somewhat more authoritative. If repl.it (at 3.7.4) allows embedding in future, that may become a better candidate for python.org, though many people still prefer the lower latency of a local machine terminal shell-like experience which the shell version suggests (perhaps even encourages with the higher latency to wait for it to load). Anyway I'm sure someone else is aware of far more detail than I can see here.

They are the star on which this guide is constructed.

From general experience, a lot of developers and engineers I've worked with acknowledge the ECMA specifications, though actually consult the MDN resource when they just want a quick overview of something as it's often simply easier than explaining the long history of the language, which is the goal here - get someone started off, without too much detail.

Please forgive my occasional OCD.

I think list() as a collection type in types/List.js (and a 700+ line implementation) would be better in an advanced guide.

Resolves an error in "make html":
/Users/pzrq/Projects/beeware/batavia/docs/how-to/tour.rst:75:Could not lex literal_block as "javascript". Highlighting skipped.