Rename unwind

[roblabla]

Unwind is already taken on crates.io for high-level bindings to libunwind., and libstd has its own unwind crate with bindings to the (other) libunwind.

[main--]

Unwind is already taken on crates.io for high-level bindings to libunwind

feels bad man, should have reserved the name when I started working on the crate (it was free back then)

So unless @sfackler is willing to give us the name (arguably not entirely unreasonable once this is somewhat feature-complete, i.e. backtrace crate also has a gimli-based backend), we need to come up with a new name. We could do something like encoding_rs, break with the convention and add the -rs to the crate name. I'm not a big fan of this idea though. But I do think a good name would a) state that this is an unwinder and b) that it's implemented in rust.

[fitzgen]

There's also pancakes, which I already reserved, and which I really like as a name :)