Throw more descriptive error when message size exceeds maximum

[t-mullen]

A common issue is pc.send throwing the cryptic TypeError: The expression cannot be converted to return the specified type (or other equally unhelpful errors) when a message exceeds the browser maximum.

We shouldn't chunk messages by default, but it would be nice to detect a message exceeds this maximum and throw a more descriptive error.

See #460, #393, #330, and others.