Make debug!, etc. macros not require a format string

r?

The one thing `log` can still do is polymorphically log anything,
but debug!, etc. require a format string. With this patch
you can equivalently write `debug!(foo)` or `debug!("%?", foo)`.

I'm doing this because I was trying to remove `log`, but there are a number of logging statements that just want to print an arbitrary value and don't care about the format string.