Port `ury-playd` tokeniser to Rust.

This should make the tokeniser behave in the correct, shell-style
manner.  Tests and upstream fixes to follow.
Update to latest rust.
Use if-let syntax.
Use #ok_or_else instead of handrolled function.

This is a new function of Option we can use!
Update locked dependencies.
Use short-hand field patterns.

Fixes some warnings with latest Rust.
Don't use unpack for testing.

Unpack (the function) is going away soon.
Remove unpack usage in core.

Unpack is no more, and the deprecation warnings are gone.  Rejoice.
Use single-quotes for packing.

This brings the packer in line with the C++ version used in ury-playd.
Also, we now use .add() instead of .push_str(), amongst other
improvements.
Move tokenisation code to baps3-protocol.rs.

Woo, modularity!
Update to latest rust again.

Argh, bit rot.
Update to latest dependencies.
Rename listmaster to listd.

Also update the README.
Missed one
Merge pull request #2 from UniversityRadioYork/mw-shell-tokeniser

Shell tokeniser, nightly updates, etc.