Remove outdated comment in the agent template.
Update .yardopts file with the new directory structure.

Notable change: only what is marked with "@api public" will be
documented.
Update the "Getting started" guide.
Fix user_api being nil during tests.
Better (and working) implementation of simulated messages from device.

Still not a "proper" implementation, but this is better.
Update docs about tests.
Merge remote-tracking branch 'origin/topic/bf_fix_user_api_in_tests' into develop

* origin/topic/bf_fix_user_api_in_tests:
  Better (and working) implementation of simulated messages from device.
  Fix user_api being nil during tests.
Merge remote-tracking branch 'origin/topic/bf_documentation' into develop

* origin/topic/bf_documentation:
  Update docs about tests.
  Update the "Getting started" guide.
  Update .yardopts file with the new directory structure.
  Remove outdated comment in the agent template.
Update ragent_bay with test and doc.
Release version v0.2.5-rc024.