I think it's time to address the elephant in the room.
This Pull Request will (hopefully!) solve part of #736.
This is a complete rewrite of `JsString`, but instead of storing `u8` bytes it stores `u16` words. The `encode!` macro (renamed to `utf16!` for simplicity) from the `const-utf16` crate allows us to create UTF-16 encoded arrays at compilation time. `JsString` implements `Deref<Target=[u16]>` to unlock the slice methods and possibly make some manipulations easier. However, we would need to create our own library of utilities for `JsString`.