Implement named arguments function calling

[ceymard]

This can't be implemented on functions that comme from javascript.

However, it would be possible for macros, filters, and tests, to have an optional signature attribute with a list of arguments and a default_args to fill up the missing attributes when not specified.

Exemple ;

exports.dictsort = (value, case_sensitive ? false, _by ? 'value') ->
   ...
exports.dictsort.signature = ["value", "case_sensitive", "by"]
exports.dictsort.default_args = ["", false, "value"]

if a call is parsed and "by" is specified, then case_sensitive still gets sent false.