[Doc] Mailbox documentation: "gets the current value of the mailbox" is confusing

[jaguilar]

Describe the issue The mailbox documentation contains language like, "Gets the current value of the mailbox." This suggests that the mailbox is a slot rather than a stream. (I hope this is not the case!)

Suggested improvement If the mailbox is a stream of objects to be read, then the language should be something like, "gets the next value from the stream of messages." If the mailbox is indeed a slot, that can be overwritten asynchronously, we should make that more explicit. Something along the lines of, "If the contents of the mailbox is overwritten by the remote peer before you read it, it is lost permanently."

[dlech]

This suggests that the mailbox is a slot rather than a stream. (I hope this is not the case!)

It is a slot, not a stream. Feel free to make a pull request with the suggested improvements.