A way to turn off indentation in the pretty-printer

@kwxm asks for a feature:

> It might be useful to be able to turn off the indentation completely. I find that largish textual programs quickly become too large and too wide to read when I prettyprint them, so I end up using `sed` to transform the output. For example, the `uniswap-3` script is `12721` bytes of flat, but when I convert it to textual form I get `24029` lines of output, the longest of them being `732` characters wide. There's a total of `10,221,880` characters, but if I delete all of the leading spaces that goes down to `105,491`, which is a bit more manageable.

This should perhaps be just an additional flag in the pretty-printing config and a carefully placed `group` calls. Although we might have `hardline`s in the pretty-printing code.