WIP - Integrate buildoutcoredevdocs

[polyester]

Integrate the documents from buildout.coredev. They are now placed under /contribute/core and have been moderated, checked for readability and relevancy.

Work in progress - a second pair of eyes is very welcome.

[stevepiercy]

For a review, I will make a new branch from this one, then create a PR against it. This is a big one, and a GitHub's web UI is not as good as PyCharm's for this. It might take me a day or two to complete.

[stevepiercy]

Just a couple of quick comments for now, more coming later.

There are a lot of whitespace reformats going on that make a review difficult. I'm going to revert the whitespace changes so I can focus on things that matter. If your editor reformats whitespace, please turn it off, as we don't have any standard and we will end up clobbering each others' editor preferences.

The submodules should never be committed to a PR.

[stevepiercy]

I give up. I don't know how to remove the committed submodules. Instead I'm just going to close this PR, and create a new branch from 6.0 with only the files from this PR.