Finish documenting `#[pallet::xxx]` macros (#2638)
Closes https://github.com/paritytech/polkadot-sdk-docs/issues/35
- Moves pallet proc macro docs to `frame_support`
- Adds missing docs
- Revise revise existing docs, adding compiling doctests where
appropriate
---------
Co-authored-by: command-bot <>
Co-authored-by: Kian Paimani <[email protected]>