Expand contexts where comma is allowed as an OR operator

[brettz9]

It would be great to expand the context in which the comma could be used (e.g., between filtering expressions to allow simultaneous matching of both an array filter and property filter as $.book[(@.length - 1), ?(@.prop == 'abc')] as well as at a higher level such as $.book,$.car) so as to better serve as an OR operator.

An implementation supporting this will probably require replacing the regexes with a genuine parser.