* Modify Doxygen grouping of `drivers` Public/Internal APIs
* Correct classification of `mbed_events.h`
* Amend name of Doxygen group containing Device Key API
* Classify `CallChain.h` as public API and relocate file
* Remove Doxygen group from `equeue_platform.h` as it has no Doxygen compliant documentation
* Move USB target specific code back to `usb/device/targets`
* Change Doxygen groups structure, splitting first by Public/Internal
This commit also does the following:
* groups the documentation of related API
* moves `events/internal/equeue.h` to `events/equeue.h`
* merges `events/source/README.md` to `events/README.md`
Separate drivers, events, and rtos internal APIs from public APIs.
* Move source files to source subdirs
* Move internal headers to internal subdirs
* Add Doxygen comments for documenting internal and public APIs
* Remove source code from header files in order to remove include pre-processor directives
that included header files not directly used by said header files
* Explicitly include header files instead of implicit inclusions via third-party header files.
Release Notes
This will break user code that was using an internal API as the internal header files have been moved.
This will only break if the user was including the header file using a namespace (i.e #include "foo/bar.h" instead of #include "bar.h"