Figure out a better way to deprecate old feature names

[sgrif]

The current way we're deprecating the various x-column-tables feature spams builds with an unreasonable number of warnings, and causes our crate to fail to compile if we have #![deny(warnings)]. Ideally we show the warning in the actual invocation of table!, but rust-lang/rust#49912 prevents us from just doing the obvious thing there.

We should find a better solution though, that doesn't spam logs, and in particular, generates no warnings from inside Diesel itself when compiled with these features turned on. The solution of "remember to remove #[deny(warnings)] when we release isn't going to work long term.