Initial Model, Statement, Storage classes
Merged new Statement, Model, and Storage classes.

Updated Description and NAMESPACE to include classes and to load in proper order.  Refactored Peter's changes to return to using initialize() methods for Node and World.  Updated tests to pass.

Merge branch 'sbpcs59-master'
Roxygen docs updated to build.

Still needs another pass at documentation to make it complete, and arrange the Rd files properly.  Collate is now generated from ROxygen dependencies, and the NAMESPACE file includes exports from ROxygen.
Ignore build artifacts.
Refactored Statement to use intitalize().

Also added barebones tests for Statement constructor.
Check that params are not NULL in initialize().

And add tests.
Refactor Storage class to use initialize().

Default Storage to use hash memory storage. Also added basic tests for Storage class.
Add test of Storage with default params.
Refactor model to use initialize().

Add basic tests of Model construction.
Add example and test of addStatement() to Model.
Regenerate Rd documentation across all classes.