When a Doxygen group has been defined (created), all its needed to add
documentation to that group is `\addtogroup`. Since all the information
about the group is preserved, it is not necessary to mention the group
hierarchy again with `\ingroup`. This PR removes unnecessary Doxygen lines
across the `drivers`, `events`, `platform` and `rtos` directories.
It also ensures that new groups are created with `\defgroup` once and
referenced with `\addtogroup` whenever documentation needs to be added to
an existing group.
* 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`
Also includes:
* rename `mbed_sleep_manager.c` to `mbed_power_mgmt.c` to match its
header file
* create Doxygen groups for public and internal APIs
* use relative path to include header files where inconsistent
* update references to internal APIs throughout libraries
* update the copyright year for all modified files