Add support for using cin files to define model-check test/comparison scenarios

[chrispcampbell]

It's common for modelers to build cin files to define different input scenarios when working in Vensim. It would be useful if those same cin files could be loaded by model-check to automatically define scenarios for check tests and comparisons. The plugin-check package could automatically load all cin files in the model folder, parse them, and define a scenario for each one. For example, if you had a cin file called test.cin that sets the value for two model constants, we could automatically have a scenario called "test" (or "test.cin") that is available in the model-check report.