add support for application/atom+xml and like content types that might begin with application/ and end with +xml
Use a regular expression pattern to parse various xml content types

and simplify the boolean expression to use less nesting, ie just
checking and not this, and not that, etcetera.
Merge pull request #444 from travisfw/master

add support for application/atom+xml and like content types that might begin with application/ and end with +xml