document the state variable

hopefully correctly
comment structure of imp

This info is in the class documentation for mids also, but this makes it
easier to interpret the code.
clarify comments

Small tweaks, including fixing a typo.
padModel function description fix

The comment was lagging behind what actually was going on.
Create README.git to describe branches.
In the future it might hold other stuff as well,
but it should all be related to git.

git does not have good facilities to attach a note to a branch, as
as opposed to a commit.   See
http://stackoverflow.com/questions/4750845/how-do-you-annotate-a-branch
Document upcoming inout branch.
Merge with master