Remove unnecessary `.to_string()`s from `Vec.swap_remove`'s doc example.
Implement len() for EnumSet.
auto merge of #18735 : utkarshkukreti/rust/remove-unnecessary-to_string-from-vec-docs, r=huonw

I don't think they're needed.
auto merge of #18740 : jbcrail/rust/implement-enum-set-len, r=alexcrichton

This commit adds the missing EnumSet method mentioned by @Gankro.

cc #18424
Try to remove ty_nil, some kind of error in exhaustiveness checking
Complete the removal of ty_nil

1) Change #[deriving] and format! to never produce PatTuple(vec![]) nodes.
2) Update librustdoc.
Remove TyBot for good from the AST representation