By removing some of the over-indenting. AST pretty printing now looks correct. HIR pretty printing is better, but still over-indents some.
Indents for `cbox` and `ibox` are 0 or `INDENT_UNIT` (4) except for a couple of places which are `INDENT_UNIT - 1` for no clear reason. This commit changes the three space indents to four spaces.
The AST pretty printing is a bit wonky. The HIR pretty printing is extremely wonky.
