Fix the post content width to be more readable

[marcus-grant]

Follow readability guide. Based on research, apparently 50-75 characters per line is optimal. This could be a bit tough with code blocks however, so let's try 80.

[marcus-grant]

Tweaked for now, this needs followup when media queries gets handled

[marcus-grant]

Move this to next release, it looks decent enough now, but to make the readability better with the properties outlined in these studies will take some creativity without filling blog-post with tons of pointless whitespace.