Add bytes per line display configuration.

I'm a fan of the configurability of the HexViewer package for SublimeText (https://github.com/facelessuser/HexViewer).

This patch adds the bytesperline configuration.
Yes, I fixed it https://github.com/AbeEstrada/atom-hex/commit/d72ec78368cde2bf182a2286b09a4ef5466bbd79