Clean slate.
Added in basic date implementation centred around "findOrCreate"
methodology, i.e. Years find months, months find days.  Still need to
add "containing" class (e.g. "Grates") that finds years.
Added "Grates" containing class that completes the "find" and
"findOrCreate" methods. Also made "find" methods in GraphMonth and
GraphYear public in order to complement the "Grates" class. Need to do
unit tests next.
Moved opening braces from own line to same line as block
declaration/defintion.
Added in unit test for basic date creation functionality. More to come.

Also added in code to check/create indices for the calendars.
Removed some silliness in the form of an extraneous static method call
to create a Grate.
Added unit tests to cover the creation of entire months and years in
graph.
Added in equality code for GraphDate.

Added in date comparison unit tests.

Adding tests for code coverage.

Code clean-up.
Updated unix date calculation to use more direct Calendar class.
Removed redundant y, m, d properties from classes. Also removed unix
date as a property and now create/persist to graph on node creation. All
lookups for unix date are done via graph lookups.
Refactored code to eliminate some duplication, mostly by pulling things
back into the AbstractGraphDate class. All unit tests pass.
Refactored again to avoid compromising hierarchical structure.
Graph-specific code now moved out of abstract class and into static
helper class.  All unit tests pass.
Changed dependence on KeyIndexableGraph to just Graph with some basic
guard code where needed.  Might need more; need to ask re
graph.getVertices(key, value).

Updated first set of unit tests to run tests through multiple graph
implementations. Currently makes use of TinkerGraph and MemorySailGraph;
might remove latter depending as it's quite different, although a decent
starting point since it does not implement KeyIndexableGraph.
Updating index guard checks.
Refactored findOrCreate* methods. All unit tests pass.
Added in date validation and associated exception. Added unit tests to
test edge cases for date creation. All unit tests pass.
Added exception for missing backing vertex. Added unit tests to test for
same and add overall code branch coverage.
Update README.md
For merge to master