Proposal: New Haddock doc format

Hey, I'd like to get everyone's thoughts on the following formatting change to the Haddocks used throughout the containers package.

## Old

- Everything on one line (for the most part)
- Complexity the first thing in the docs (important, but not THAT important)
- Examples expanded by default


## New

- First line is a one sentence summary
- Followed by longer description with more details on args and caveats
- "See also" line
- "Complexity:" line
- Examples (collapsed by default), description of example followed by code and output