Please add text(s) of license file(s)

[krasimirgg]

The license field in Cargo.toml indicates that this package is licensed under "MIT/Apache-2.0". It's good to have the license(s) text(s) in the repository as well (and into the cargo package) so this work can be properly attributed downstream.

Example from hashbrown, a crate that's licensed under MIT or APACHE:

• https://github.com/rust-lang/hashbrown/blob/master/LICENSE-APACHE
• https://github.com/rust-lang/hashbrown/blob/master/LICENSE-MIT

[Gankra]

landed in #53