v0.3

Some bug fixes and improvements:

• All commands should now complete attribute paths when supplying '<nixpkgs> as file input
• nix-env: -A only worked for -i/--install, now works for all main operations
• nix-env will now only complete main operations until one has been supplied
• nix-env --switch-generation will now complete generations
• nix-channel: completes channel names properly now

And a few other minor improvements.