Devdocs reorganisation (#913)

* docs: split usage and dev docs

* # This is a combination of 2 commits.
# This is the 1st commit message:

docs: split usage and dev docs

# The commit message #2 will be skipped:

# fixup add docs

* docs: add runner documentation and move hooks documentation to devdocs

* docs: add stubs for modules technical description

* docs: add paragraph about event thread-safety

* docs: add 'Current modules' section header

src/modules/example_powertoy/README.md

@@ -1,22 +0,0 @@
-# Example PowerToy
-
-# Introduction
-This PowerToy serves as a sample to show how to implement the [PowerToys interface](/src/modules/interface/) when creating a PowerToy. It also showcases the currently implemented settings.
-
-# Options
-This module has a setting to serve as an example for each of the currently implemented settings property:
-  - BoolToggle property
-  - IntSpinner property
-  - String property
-  - ColorPicker property
-  - CustomAction property
-
-![Image of the Options](/doc/images/example_powertoy/settings.png)
-
-# Code organization
-
-#### [`dllmain.cpp`](./dllmain.cpp)
-Contains DLL boilerplate code and implementation of the [PowerToys interface](/src/modules/interface/).
-
-#### [`trace.cpp`](./trace.cpp)
-Contains code for telemetry.