Multi-line string support with stripped indentation

I would like to switch from neat-interpolation because string-interpolate is better in every way. The only reason I haven't is because I need support for multi-line strings where the indentation (and leading and trailing newlines) are stripped.

My program uses a lot of multi-line strings for human-consumed error messages. Currently they are written like this with neat-interpolation:

someMessage :: Text
someMessage =
  [trimming|
    This is an example error message.

      Some key:    Some value
      Another key: Another value

    This will be posted in something like a GitHub comment or email, where I value using multiple lines and padding.
  |]

With string-interpolate, I would have to write them like this to ensure I don't have any extra whitespace:

someMessage :: Text
someMessage =
  [i|This is an example error message.

  Some key:    Some value
  Another key: Another value

This will be posted in something like a GitHub comment or email, where I value using multiple lines and padding.|]

This gets even uglier and harder to read when the quasiquoter starts more indented (e.g. inside a where clause) because I'm forced to start new lines without any indentation. I also can't use the iii quasiquoter because then I would lose my newlines and padding.

Would you consider adding back the __i quasiquoter? I see that you decided against adding it in this PR: !21 (merged). But I feel like this is one of the most common use cases for these multi-line string interpolation libraries.

I think the most intuitive behavior for a __i quasiquoter would be:

1. Strip leading and trailing newlines (anything bumping up against [i| and |])
2. Strip leading indentation, using the least indented line as column 0

Basically what neat-interpolation is already doing with its trimming quasiquoter.