Lexical ANTLR description for financial quantities in American notation, like $**2,345.67 $12,452,183.16 $****12 $*0.124300
Note that there is a dollar sign at the beginning, optional asterisks follow,
next we have a natural number without leading zeros and with a comma separating
every three digits starting from the right, and finally there is an optional
“.” followed by one or more digits.
Guillem Godoy (taken from Jordi Cortadella's exercise list)