function str2enum( dtype ) {
	var v = ENUM[ dtype ];
	return ( typeof v === 'number' ) ? v : null; // note: we include this guard to prevent walking the prototype chain
}
Returns the enumeration constant associated with an ndarray data type string.

## Notes

-   Downstream consumers of this function should **not** rely on specific integer values (e.g., `INT8 == 0`). Instead, the function should be used in an opaque manner.

@param {string} dtype - data type string
@returns {(integer|null)} integer value or null

@example
var v = str2enum( 'int8' );
// returns <number>