Statically assess data integrity.

[totherik]

Currently the state language definition is validated for structure using JSONSchema, but no validation of data integrity is done, e.g. StartState and subsequent Next states are not validated prior to running the state machine, etc.

This would be useful to ensure a machine can be run to completion prior to invoking it.

[totherik]

step/src/states/index.js

Lines 26 to 35 in 381065d

	if (!task) {
	/**
	* TODO: https://github.com/totherik/step/issues/1
	* This should not be done at runtime.
	* Also, don't abandon the existing promise chain, so
	* procced, break the while, and return.
	*/
	const error = new Error(`State "${name}" not defined.`);
	promise = promise.then(() => Promise.reject(error));
	}