function str2enum( operation ) {
	var v = ENUM[ operation ];
	return ( typeof v === 'number' ) ? v : null; // note: we include this guard to prevent walking the prototype chain
}
Returns the enumeration constant associated with a BLAS operation side.

## Notes

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

@param {string} operation - operation side
@returns {(integer|null)} integer value or null

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