Documentation issues

[MichielStock]

There are several issues with the documentation:

• The views of the HVs do not match the provided output since feat: hypervector string representations #30
• The example in the docs on ngrams does not yield the correct result. I find it hard to follow and debug.

[cvigilv]

mmm, that's weird. I'll update the documentation to check what's up with that, maybe the ngrams function is incorrect (and I could make use of our new encodings, that part of the tutorial is a little outdated).

[cvigilv]

Related to #32