Add converter from cql #82
Description
There's probably quite a few cql (not cql2) examples out there in the wild, e.g. stac-utils/rustac-py#135 (comment) was taken from a cql example. It could be handy to provide a converter from cql to cql2 as a part of this library. If there's a grammar for cql, maybe it wouldn't be too big a lift.
I envision the Rust crate just providing the conversion methods, and any downstream Python clients (either this one, rustac, or whatever) could link together the conversions in to nice "fallback" behaviors as they see fit.