Handling of Apache "NOTICE" file

[nicopap]

Currently cargo-about doesn't really comply with the Apache-2.0 license. Apache has a whole section introducing and specifying how to handle NOTICE files (4.d) , I see no handling of NOTICE in cargo-about. I've read about 10 times the NOTICE section and it seems that having a reproduction of all the NOTICE files is required; though IANAL.

Someone using cargo-about will be in contravention of the conditions of the Apache license if any of their dependency has a NOTICE file. The legally conscientious user will need to manually go through all their Apache-licensed dependencies dragging for stray NOTICE files. This undermines a major functionality of the plugin.

Solution: implement NOTICE handling by concatenating them and adding them to the output of cargo about generate.