Object.each() and Object.invert()

 - Both functions work staticly and as instance meathods.
 - Both functions have tests and docs.

 - Object.each() could replace Object.create(obj).keys().each(...) which is
   all over.  It also has the benifit that the values don't need to be looked
   up.
 - Object.each() suports early exits, and returns the value.

Closes #298.