Increase usefulness of the retry component compile errors

Adjust the descriptiveness of the errors raised when a
retry atom is used in a flow or as the root item of a
to help users understand why the error is raised.

Change-Id: Ia3e13382d49e2225d48b2ae875061f92c211093c
Rename additional to general/higher-level

The wiki really contains the general/overview and
higher-level information and the developer documentation
should reflect this (instead of just saying additional
documentation is located there).

Change-Id: I4ac58aac6ec61b11f4507a7c51973e0b492c5ade
Add example for pseudo-scoping

Add an example how to use flow factories and prefixing to achieve
effect similar to scoping, but without it.

Change-Id: Ia587ad59f76a0dd477dba79c24e5f86f4b4a34ba
Merge "Rename additional to general/higher-level"
Merge "Add example for pseudo-scoping"
Merge "Increase usefulness of the retry component compile errors"