implement support for bits per sample

[Nemo64]

With this change, wave files with less than 32 bits per sample work correctly. I took a bit of special care for the 24 bits per sample situation.

I'm also not sure why signed integers don't seem to play a role. But it worked. Here a beautiful 24 bit wav file visualized

This also solves https://github.com/boyhagemann/Waveform/issues/7

Since this library is unmaintained, I'm going to use my own repository branch "all-fixes". But I'd like to be prooven wrong @boyhagemann ;)