Library Functionality Complete

Opening this pull request under my personal account to get this code somewhere other than my laptop.

All the library functionality is complete, but there is no CLI parsing yet, so the library must be utilized through handwritten Ruby scripts. Locally I have scripts to expand the product, customer, and transaction data. It's pretty straightforward… you just define `Column` objects which specify the generation and conversion strategies for each column. Then you read in existing data and it passes it through before generating a certain number of new rows based on a `factor` parameter you provide.

Needed:

  * A better name for an actual open-source dump
  * User-facing documentation
  * Null value logic (right now we throw away bad rows entirely)
  * Logic to make new columns based on existing ones (denormalization features)
  * Progress indicators?
  * Licensing

This comes with 100% test coverage, at least for now.

/cc @bredman in case you want to see any of this