feat(pattern): Add a bold line every N squares

[oktak]

TODO: fixes #3

1. added adding bold lines for pattern
2. since I am using Windows /_, so I added some platform specific for my test.

[acrosman]

This is a great start on #3 and is the right basic idea, but there are a couple issues.

The biggest being that ideally the count would carry over page to page, so that if printed and lined up again you could use these bold lines as counting guides all the way across the pattern. So if the page 1 is 45 squares wide, the page that lines up to be the next to the right (usually during testing that's page three) would off-set this so that first box starts shifted over the same 5 squares.

The windows file path handling is fine for now until I get around to handling #8.

[oktak]

I see, that means the bold lines should be continuously counting page to page?

Let me think how to implement this ;)

[oktak]

3b3893d would offset the bold lines by the residue of adjacent pattern.
Please see if it works as you think :D