Remove markup from help_usage string.
Pass the right synopsis string to MainArgParser.
Support escaping and quotes for shorthand params

Add support for::

    --foo key=one,value=one\,two\,three
    --foo key=one,value="one,two,three"

Note that for the escaping case, in bash you'll have to
literally type '--foo key=one,value=one\\,two\\,three'
because bash will also interpret the '\' char so you have to
escape the '\' so bash will leave it alone.
Use six compat for advancing iterator

iter.next() not in python3.
Fix test to acutally check quoted return value

Split them into separate tests as well.
Allow for single quote chars in csv values

In windows, users have to use single quotes because
cmd will consume the double quotes before it hands the
args to python.