Use inclusive terminology [1] to eliminate 'master' and 'slave' terms as
much as possible from code and documentation. 'master' has been changed
into 'main' and 'slave' into 'subordinate' or 'sub'.
After this change, some references to the 'master' and 'slave' word can
still be found in repository:
* `slaves` sub-command of `interp` Tcl command
* `--slave` option of `update-alternatives tool in RPM spec file
* `master_doc` attribute of Sphinx `conf.py` file
* git 'master' branch need to be renamed and tools referring it need to
be updated accordingly (configure, script/mpub, script/mrel)
[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=49decddd39e5f6132ccd7d9fdc3d7c470b0061bb