Thin collections for Rust 0.5.3

• Fix appending an empty ThinVec to another

Thin collections for Rust 0.5.2

• Fix zero-length slices from ThinVec

Thin collections for Rust 0.5.1

• Allow ThinVec::transmute to use non-Copy types.

Thin collections for Rust 0.5.0

Alternative implementations for vector, map and set that are faster/smaller for some use cases.

Initial release.