v0.4.4-beta.2 Bin width fixes

Fixes #21 - which helpfully contains no information about the issue.

Basically by not rounding the calculated CNV bin_width, we were duplication the difference between the nearest 1000 (rounded up) and the acual base number for each bin, resulting in contigs which were too long when plotted via

bin_width * number_of_bins

So this has been fixed by rounding the CNV bin_width to the nearest 1000 and using that throughout the calculations.

Adds documentation for the keyword arguments as well.

If confirmed working, will be ready for merging the PR and full release.

Needs the changelog updating!

Full Changelog: v0.4.4-beta.1...v0.4.4-beta.2