Fix and clarify license in crate metadata and add missing license files

[decathorpe]

I am responsible for packaging some crates from this project for Fedora Linux, and have noticed that there are some issues with the license metadata / missing license files in published crates. I see that there are also reported issues for this (#912, #972, #1249), and attempted to fix the issues reported there, and some issues I noticed myself:

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It appears that the project was intentionally relicensed from BSD-3-Clause to Apache-2.0 in commit d81a895, but this was, at least in part, not updated in crate metadata. This results in crates.io and tools like cargo-license to show the wrong license for some crates in this project. To address this, I adapted the package.license field in Cargo.toml files for the nalgebra, and nalgebra-glm accordingly.

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The nalgebra-lapack crate is MIT licensed (there is a license file for the MIT license included, and the documentation agrees), but the crate metadata claims the crate is BSD-3-Clause licensed. Maybe this is a copy-paste error from when the crate was originally imported? To address this discrepancy, I changed the package.license field in Cargo.toml from BSD-3-Clause to MIT.

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One of the terms of the Apache-2.0 license is that any (re)distributed sources contain a copy of the license text. This is currently not the case for the nalgebra-glm, nalgebra-macros, and nalgebra-sparse crates. This is problematic for Linux distributions that package these crates, and potentially also for publishing them on crates.io. Adding a symbolic link to the LICENSE file from the project's root directory should cause cargo package / cargo publish to properly include this file when publishing.

[sebcrozet]

Your analysis checks out. Thanks!

[decathorpe]

Great - thank you! 🎉