Repeated sections and code

[devjsc]

I found a bit of repeated code examples and sections in Options for running your Agents, Agent Mailboxes, Agent Functions, and Make your agents AI Engine compatible. I found this a bit confusing to follow. I think it would be better to merge these 4 sections into less sections, without the repetitions.

[devjsc]

cc @ManueleSigona

[devjsc]

Repeated sections of content are a necessary evil, we can't assume that people are reading every page in sequence, so we lightly reintroduce concepts where needed. I don't think we'll ever get this perfect, but hopefully our rationale makes sense.