Let's write a unit test! and "Post modern C tooling" updates.

A new version of the 4000.zip has been uploaded with some updates.

Firstly, I worked on the "Let's write a unit test!" chapter. Added a couple of example unit tests for it. It's also about how to work with git and github. More specifically it guides the reader through making a small change to the pygame repository, and then pushing a "Pull request".

One comment I got on the draft was that there was not enough explanation of some of the terms. So I started a section to describe what things like 'git', 'pull request' and such are to people who are not familiar.

Then I added a whole new section to the book on "Post modern C tooling".  This is one I've been writing and researching quite a lot, and this has already gone through several drafts. Using C is much easier with appropriate tools, so this is very useful for a working C programmer. Unlike with other languages, you REALLY need extra tools when working with C.