Made `std::option`and `std::result` more similar

This takes the last reforms on the `Option` type and applies them to `Result` too. For that, I reordered and grouped the functions in both modules, and also did some refactorings:

- Added `as_ref` and `as_mut` adapters to `Result`.
- Renamed `Result::map_move` to `Result::map` (same for `_err` variant), deleted other map functions. 
- Made the `.expect()` methods be generic over anything you can
  fail with.
- Updated some doc comments to the line doc comment style
- Cleaned up and extended standard trait implementations on `Option` and `Result`
- Removed legacy implementations in the `option` and `result` module