Made std::optionand std::result more similar

[Kimundi]

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

[alexcrichton]

I think that we shouldn't take renaming of option methods very lightly any more. Has the transition from map_default to map_or been discussed and agreed upon?

Also in the future, I know it's tough and I always forget to do this as well, but it's always nice for reviewing if reorganization of code is separated (by commits) from refactoring/renaming and additions to code. It's tough to see here that the only method on option that changed is map_default. I'd be interested in the amount of fallout that the change had, but right now it's all mixed in with the Result changes as well.

Other than that though, I like how this pretty much makes the apis of option and result the same. I'm in favor of all the changes to Result, I think that map_default may need more discussion though.

I'd r+ a pull request which didn't modify map_default though!

[thestinger]

We previously came to the consensus that using default for methods unrelated to Default should be changed.

[Kimundi]

I updated the PR to not include the map_default -> map_or change for now. I'll make a separate PR for that once this lands.

[alexcrichton]

I talked with @Kimundi on IRC, and I like where this is going, but I'm personally a little uneasy about all of the err_* variants of functions. He's going to go play around with the idea of a fn ok(self) -> Option<T> function and see if we can reduce the surface area of the api here.

[Kimundi]

@alexcrichton: A buildbot failed with a runtime abort, so I used the additional time to update this PR with as much cleanup as possible without touching the _err functions