Automatically determine sample level based on text length for short text

[faassen]

The following constraint exists on sampling level:

2^L < N

where L is the sampling level, and N is the size of the text. At least that's what the error says.

This means that a sampling level of 2 must have N > 5, and a sampling level of 1 requires N > 2.

Strangely enough I think it requires level 0 to have N > 1, but in #23 I report I can make a size of 1 work with level 0? I don't understand why I didn't get this error.

It strikes me that it would be possible to automatically reduce level if the text is too short to sample effectively anyway. That way we don't bother people with this error. We could write that this happens in the documentation. It would make the library more ergonomic to use.

[faassen]

Ah, I see in #23 I couldn't make it work with just a \0. Not clear whether I could make it work without a \0, but since the \0 is required at the end that's fine.