core: Rename container to collections. Closes #12543

[brson]

Though I'm sure there are more things to change about the collections traits, this solves the specific complaint in the linked bug by using "collections" consistently.

[brson]

Oh, these are all breaking changes. I'll update.

[alexcrichton]

This may not be quite the change that we want. I think that in an ideal world the entire container module would move into libcollections. The collections library currently has one generic trait Deque (which is of questionable quality).

I'm only hesitant because if that's our long-term goal then I don't think this is moving us any closer to that (we'll still have to rename all imports). The renaming of Container to Collection will probably stay, however.

[brson]

OK.

[liigo]

One letter longer (Container -> Collection)

[alexcrichton]

Due to the movement of libcollections, I take back what I said about all imports being renamed. All imports will be renamed to std::collections::Foo anyway (sorry!). I'm working on a rebase of this.