Parser fails on bare identifiers containing a prefix matching a keyword

[Ben Reinhart]

Legal bare identifiers with a prefix that matches a keyword cause the parser to return errors. I submitted a PR with test cases to the main repo to help test the desired behavior.

Existing behavior

The following examples all return errors

kdl.parse("null_id");
kdl.parse("node null_id=1");

kdl.parse("true_id");
kdl.parse("node true_id=1");

kdl.parse("false_id");
kdl.parse("node false_id=1");

Expected behavior

The above examples should return a valid document with valid nodes.