updates to the kmeans series

A bunch of minor changes. Not sure what's up with the github diff, but you may want to run `git diff -w` locally to see the non-whitespace diff..

I have two comments that I did not address in the commit.

1. You have a tendency to narrate the code, by which I mean you insert snippets of the code you are describing between clauses of your sentences. I think this is ok in small doses, but it can make the text quite difficult to read when taken too far (specifically at the end of Part I).

2. The css for the code snippets needs some fixing up. A lot of the snippets stretch out of the block and become impossible to read against the light background of the page. I played around with the css a couple weeks ago and was able to add a scroll-bar, but then the type popups became stuck inside the block and were obscured. There should be a way to hack around this issue, but my css-foo is not particularly strong..