Merge pull request #449 from checkcheckzz/master

add Mule description
Improve Which Python section grammar
Merge pull request #450 from ceaess/master

Improve Which Python section grammar
Two easily.
Some grammar fixes for writing/structure.
More grammar and cross reference for #132.
More writing/structure changes.
Grammar and a couple line wraps for writing/style.
Added pep-3132 style extended unpacking.
Mostly line wraps, and a small grammar fix to writing/documentation.
Minor fixes for writing/tests.
Two minor changes to writing/gotchas.
A single wording change in writing/license.
Merge pull request #456 from george2/grammar-and-typos

Grammar and typo fixes
Merge pull request #455 from george2/extended-unpacking

Added pep-3132 style extended unpacking.