Suggest a suitable value for the parameter m

[jermp]

Even if set, users should be notified about suitable values for m.
As documented in the papers, m should be chosen >= log_4(N)+1, where N is the cumulative length (num. bases) of the SPSS but the software does not currently output this value.

So, if users set m to something below the recommended value, they should be notified.

We can the file and compute N; or we can just stat the file and get the size in bytes, although this works only for uncompressed files.