Don't use hard tabs

[keiranmraine]

Markdown linters don't like hard tabs by default. Could the code be changed to use spaces instead (converted to 4 spaces according to github flavour markdown spec)

[joshbader]

I would personally like an option for 2 spaces. Maybe make this a setting?

[Merovex]

I am running into a problem where the tab is creating a PRE block in the two markdown converters that I use.