Per the grammar (`decimal := integer ('.' [0-9] [0-9_]*)? exponent?`), underscores in the fraction part should be allowed (as in `node 1.0_2`, the contents of the corresponding input file), but there was no expected_kdl file for this test case, indicating it's supposed to be a parse failure.
I'm assuming this was a mistake, since underscores in the fraction part make complete sense (and are allowed in the other two parts of a decimal number).
/ is not a valid identifier character. This updates
unusual_chars_in_bare_id.kdl to only include unusual but valid
identifier characters, and adds separate invalid input tests
for non-identifier characters.
Fixes#166