Merge pull request #1 from spmallette/master

Tests Passing
Improve graph comparison test

Extend graph comparison test to check edge counts for vertices, in/out vertices for edges, and properties for both.   Make comments in metadata read/write code clearer.
Minor refactoring to make variable naming consistent
Refactor tinkergraph metadata reader and writer code to separate classes

Add tests for tinkergraph metadata reader and writer classes
Introduce TinkerFile interface and factory.

TinkerFile and TinkerFileFactory encapsulate different file storage approaches.