Give information about unsafe keyword on crate readme metadata

[ikhwanperwira]

As the philosophy of rust is being memory safe, every crate that published by cargo must tells info whether the crate is using unsafe keyword or not. So that the publisher no need to manually give warning and another people can consider to use the crate or not. The dependents must be affected too.

This can be easily solved by rust-analyzer or cargo where the cargo analyze the entire code and check whether it found unsafe keyword or not.

The only exception to remove mark unsafe even thought using unsafe keyword on a crate is, if there are consensus on another third party to confirm that the crate is safe to being used.