#119 Issue

- implement incr,decr,add-assign,sub-assign on object property

- added tests
LetStatement implement new functions

- added support for assign and concat-assign for object property

- added testsadded test for it
LetStatement implement new functions

- added support for object property mul assign (*=)

- added test for it

- fix parser mult-assign to mul-assign
Merge pull request #138 from zaets28rus/119_let_statement_on_property

#119 Issue