Handle variadic arguments

[judu]

Variadic arguments are implemented like this:

• Allow arguments that are not declared. Parse them as strings.
• Keep the args field which now contains all the args.
• Add two more fields: namedArgs and unnamedArgs.
• namedArgs is an object {argName: argValue} with all the declared args. Declaring the args puts their value in this object accessible with their names.
• unnamedArgs is an array containing all args except the ones in namedArgs. In case you want to iterate over the undeclared args only.

close #7