A data structure used for storing and validating [decision tables][1].
Features:
* each column has its own set of (string) values
* add and remove rows
* check that the table is complete (that is, has every possible input row)
Roadmap to v0.2:
* arbitrary output types
* "don't care" cells
Future:
* Range cells
* Multiple input types
* CLI
* Find missing inputs
[1]: https://www.hillelwayne.com/post/decision-tables/