Fork of std::collections::HashMap

A fork of Rust's std::collections::HashMap type that has some minor changes. This fork only exists as a band-aid until the changes are implemented in Rust's stdlib.

Changes

• Added HashMap::take which is the same as HashMap::remove but also returns the key.
• Added HashMap::entry2 to take a Cow key.
• Added ::key to the various Entry types

Forked from d1c7a93eff5bd27632130cc5bcdaac54c32bca08