updated CHANGELOG and fixed URL x.y.z issue in docs.
added UnionStep, UnionLinearStrategy, CapTraversal (for the cap() method like count() and CountTraversal). Merged in @rjbriody TraversalHelper.hasStepClass() to try and make Stragegy execution as fast as possible.... no need to make lists if they will simply be empty. Fixed #73
added union() step documentation to asciidoc with new image.