Solves the license issue (#5)

* Add Apache-2.0 license file

* Add MIT license file

* Update relevant files with license information

Author: charleschege

Cargo.toml

@@ -3,7 +3,7 @@ authors = ["MathxH Chen <[email protected]>"]
 description = "A Simple Publicly Verifiable Secret Sharing Library"
 edition = "2018"
 keywords = ["pvss-scheme", "secret-sharing", "threshold-cryptography", "zero-knowledge-proof"]
-license-file = "LICENSE"
+license = "MIT OR Apache-2.0"
 name = "mpvss-rs"
 readme = "README.md"
 repository = "https://github.com/AlexiaChen/mpvss-rs"