Make names clearer around function bindings and bind statements

[fitzgen]

I keep wanting to refer to both of them as "bindings" and I think we could wordsmith some better names to make things more clear.

On IRC, @lukewagner suggested

• "function bindings" -> "coercion functions"
• "bind statement" -> "export binding" or "import binding"

That seems like an improvement to me.

[Hywan]

Agree on the suggestion.

[lukewagner]

Ok great. There is probably a big explainer refactoring necessary for ☃ Bindings, so this can be included as something to be fixed.

[pchickey]

Closing as out-of-date: the proposal has evolved into Interface Types since this was opened, and these particular names are no longer around.