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
Macro MBED_DEPRECATED_SINCE is defined in platform/mbed_toolchain.h which was not included.
If someone used member functions lock or unlock (which are prefixed with MBED_DEPRECATED_SINCE since some time), there would be a compile error instead of a warning.
Including mbed_toolchain.h fixes that.