Change indentation to 2 instead of 4

[terlar]

Currently the indentation is using 4 spaces, which is not aligned with d2 fmt (which is using 2 spaces).

Perhaps we should change to align or make it configurable.

[MoisMoshev]

It's true that the width is hardcoded currently. I think normally it is a configuration variable in other modes.

[andorsk]

Addressed in #52