__set__ returns an 'undo' function that when invoked will restore the module to the values it had before it was called
added __with__ function according to proposed syntax in issue #29
Refactor code to match module style
Move __with__-function into own module
Refactor tests
Improve __with__ tests
Add promise feature to __with__
Add __with__ to excluded files
Merge branch 'bobpace-undo'
Adjust README