Kmerdb

Build system migration completed. Closes 109. Completes triage of the hotfix rebase. Old master abbrogated.

Migrating to a new wheel generation process using `python -m build`. `pyproject.toml` Generates a working installed module `kmerdb`.

This can be confirmed by running
python
$ python
>>>import kmerdb


Similarly, direct module invocation works fine, this minor release is bugged because of the `pyproject.toml`.
bash
python -m kmerdb -h

Adds parallelization support to the Cythonized distance function 'pearson'

`kmerdb distance -p 10 pearson inputs.tsv`

Minor documentation changes, some refactoring/renaming.

Minor bug fixes, patch to the Cython extension to use an 80-bit floating point accumulator.

This is release v0.6.7, which includes a Cythonized function to calculate the Pearson correlation coefficient, identically to before, just with Cython and long arrays.