Raise compiler errors when bot configuration is invalid

[cjlucas]

Ideally we would raise a compiler error if the bot is misconfigured in some way. Here's a few things we could raise errors on:

• If a channel block was defined outside of a network block
• If the given handler for an event doesn't have an arity of one
• If required configuration is not specified. For instance, a server must be specified in a network block.

[cjlucas]

The above examples are enough to mark this ready for dev. This is mostly about understanding the limitations (if any) and setting up a simple system for raising compiler errors.