Added ornl.elision.core.AtomWalker that implements the visitor pattern for basic atoms, and added an AtomWalker.eli to play with it.  Closes #115.
Merge pull request #116 from sprowell/master

Implemented Visitor
Added Easter Egg.
Cleaned up some comments and changed the type of some of the well-known operators.
Merge pull request #117 from sprowell/master

Minor Changes