add new Expression
add new Expression
add benchmark tests for new Expression class
add operators (callback, combine, comparison, logical, parameters) without tests
add Path operator
rewrite Lambda
tests for Lambda (fix bugs)
static usage of Lambda methods, eq. Lambda::_x() is identical to (new Lambda())->x()
* remove old Expression classes
* now Linq\Expression\Lambda inherits new new Lambda class
implement empty(), defaultIfEmpty()
optimize Lambda expression