Rename package to sknnr and prep for alpha release

[aazuspan]

Closes #61 by updating all references from scikit-learn-knn-regression to sknnr. Also preps for the 0.1.0-alpha release by updating install instructions and the package version.

[grovduck]

Looks great, @aazuspan. Out of curiosity, did you use hatch version 0.1.0-alpha to change the version or edit __about__.py directly?

[aazuspan]

Out of curiosity, did you use hatch version 0.1.0-alpha to change the version or edit about.py directly?

Good question. Based on pypa/hatch#697 it looked like setting a non-standard version wasn't going to be straightforward with hatch, so I just edited it manually.