Ensure correct dependencies license information is included

[Nemo157]

#38 added a subcommand to print cargo-lichking's dependencies licenses using the new bundle printing functionality. Unfortunately this is very easy to have incorrect, and even with the test added in #48 will be incorrect if someone builds without using the lockfile (which includes via cargo install).

One way to do this would be to provide the main functionality via a library, which can then be used as part of the build script to generate this file for the current build. That will probably double the already quite long build time though....