Allow spaces and special characters within class and field names

[dwhatley19]

The following two examples of syntax are unparseable by snapdown.peg.js:

a -> (char[] 0 -> 't', 1 -> 'r', 2 -> 'u', 3 -> 'e')

a -> (char a[] -> 't', 1 -> 'r', 2 -> 'u', 3 -> 'e')

Need all types of special characters within class, field, and variable names to be parseable.