'goal sitegen' tweaks inspired by eyeballing more Pants doc pages

Don't insert pilcrow anchor in the heading; instead, lay it nearby with a table. Otherwise, it looks funny if the line breaks right there.

Add a "Generated by publish_docs dist/markdown/html/README.html 2014-10-17T11\:16:07.253750" so that folks who are looking at a doc from two years ago have an inkling of the danger. And/or if they want to fix a mistake, they have a clue where the content came from.

Widened margin around the page-level table of contents.

Testing Done:
https://travis-ci.org/pantsbuild/pants/builds/38290410

Reviewed at https://rbcommons.com/s/twitter/r/1178/
Sync of https://github.com/pantsbuild/pants/commit/dcde55606e7cab2aa7e14beb309387ec63378924