function isStartcase( value ) {
	return ( isString( value ) && startcase( value ) === value );
}
Tests if a value is a startcase string (i.e., the first character of each word is uppercase).

@param {*} value - value to test
@returns {boolean} boolean indicating if a value is a startcase string

@example
var bool = isStartcase( 'Beep Boop' );
// returns true

bool = isStartcase( 'beep boop' );
// returns false

bool = isStartcase( 'beep and boop' );
// returns false