Fix problem with parsing parenthesized expressions
Fix problem with parsing parenthesized expressions

Since identifiers were allowed to contain parentheses before this fix, it was
not possible to parse a parenthesis expression that lacked whitespace between
the opening paren and, e.g., the following identifier. Now, by disallowing
parentheses in the identifier itself, the problem is averted.

ronichoudhury-work/resonantlab,ronichoudhury-work/resonantlab,ronichoudhury-work/resonantlab,ronichoudhury-work/resonantlab