copy changes and typo fixes for docs

I did a pass through the docs, running example commands and comparing command line args with help, then updating the corresponding files.

I found some of the targets referenced in the text had changed, so I updated the commands associated. Where the contents of the files had changed, I updated the text to reflect the new code.
Pin pants support down to python2.7 - dropping 2.6.

Testing the python3.3+ waters will happen seperately - this just drops support for running pants against 2.6 as agreed.

Testing Done:
CI away here: https://travis-ci.org/pantsbuild/pants/builds/40110691

Bugs closed: 722, 767

Reviewed at https://rbcommons.com/s/twitter/r/1278/
Skip compressing/writing artifacts that are already in the cache