Improve checker logic and error messages

[ChrisZYJ]

I think the current m_checker.fpp contains some logic that is not perfect, and some messages are not clear to the user about what's wrong or what value should be used in the input file. An example would be:

        elseif (weno_eps <= 0d0 .or. weno_eps > 1d-6) then
            call s_mpi_abort('Unsupported value of weno_eps. Exiting ...')

I can work on this if needed.