This rewrites the commit aa7e1bff.

Refers to #86.

Shows OK in green and FAIL in red

Thanks to @frakman1.

Refers to #81. Needs fixing `test_stdout()` in the unit-test.

By the way, don't add `if arch` for checks that require 'is not set'
(there is nothing wrong with that).

Drop `> /dev/null` for non-verbose output of the tool.

It always runs as a main program.

This file was made with root privileges, so it has a full list of sysctls.

The GitHub Actions virtual machine has such a sysctl:
  fs.binfmt_misc.llvm-14-runtime/binfmt = enabled

This example shows that sysctl names may contain the / symbol.

Refers to #65

Refers to #65