Rename the AssigningExpr class to AssignmentExpr

Add provision expression

Add the NArgExprJsonBuilder class

Запрос на слияние 'json-builder' (#2) из json-builder в main

Add expr json-based builder

Add expr json-based builder

Запрос на слияние 'arg-order' (#1) из arg-order в main

Correct argument order and add default argument values of constructors of some classes

Correct argument order and add default argument values of constructors of some classes

Improve empty expr sequence exception raising mechanism

Add expression sequence

Add assigning expression class

Add exception-catching and validating expression classes