hashCode implementation for Parameter class.

An existing implementation of Parameter.equals exist without
having an implementation of hashCode(), this violate the requirement
that equal must have an equal hashcodes.
GraphMLReader did not properly type cast properties.

Change the key type map so that it used the id per the graphml spec.
Upgraded to jackson 2 and fasterxml namespace. #350
Updated changelog.
Merge remote-tracking branch 'upstream/master'