Add support for '$' as an identifier character

[mww-aws]

JKind is often used for translation from other notations and one difficulty is that it is often necessary to introduce new identifiers during translation (along with the identifiers from the problem being translated). There is a risk of name clashes for the new identifiers. I would like to allow the use of the '$' character in identifiers to facilitate creating these fresh identifiers without name clashes.

Examples of valid identifiers with the addition:

foo$bar, $theOneRing x$