improved 2-args macro to support both syntaxes
improved 2-args macro to support both syntaxes

both `--long-commmand=arg` and `--long-command arg`
are supported by macro `NEXT_FIELD()`
so that the long-command only needs to be listed once.

This extends the syntax to support new syntaxes like
`-o=FILE` or `-D=dict`,
though there is no need to advertise this capability for the time being.

Also : added `NEXT_UINT32()`,
which is wrapper around `NEXT_FIELD()`
to read integer parameters.
Use the wrapper to new field, such as `--memlimit`
which can now support both syntaxes too.

Cyan4973/zstd,Cyan4973/zstd,Cyan4973/zstd,Cyan4973/zstd,Cyan4973/zstd