use joda-time for < java 7 compatability
Change rack id in test from number to a string to avoid confusion
Some cleanup of the constraint code, bug fixes along with tests
Document the meaning of the different contraint operators
More constraints cleanup
Update examples
Merge pull request #155 from mesosphere/constraint-fixes

Constraint fixes
Merge pull request #154 from rloomba/joda-time

use joda-time for < java 7 compatability
Add Java client