Bug fixes and documentation improvements

	modified:   src/main/java/edu/ucla/sspace/graph/ChineseWhispersClustering.java

- Fixed bug where the clustering output was reversed in the MultiMap.   Output is now cluster-to-items

	modified:   src/main/java/edu/ucla/sspace/util/KrippendorffsAlpha.java

- Rewrote the class to use the co-incidence matrix

- Interval code now works.  The bug was in the difference function due to
  misinterpreting the summation: should be sum(x_1) - val instead of sum(x_1 -
  val).

- Still need to do a clean up of the class, as it is now a mess with three
  half-implementations

	modified:   src/main/java/edu/ucla/sspace/util/WorkQueue.java

- Fixed javadoc with how create a new instance

	modified:   src/test/java/edu/ucla/sspace/util/KrippendorffsAlphaTest.java

- Added new unit tests from Wikipedia
Cleaned up alpha code and prepared for final commit