Remove namespaces from tonic

The behaviour of namespaces in tonic conflicts with the precedence behaviour of bind discussed in #82 (closed). This is confusing and complicates value resolution logic.

In addition, we don't have any concrete use cases for namespaces yet, and in principle one can anyhow emulate them by extracting the scoped behaviour to a function. We should remove them from tonic until we're able to come up with a real need for them.