Add zlib licensing option

Cargo.toml

@@ -8,7 +8,7 @@ authors = [
 ]
 homepage = "https://github.com/grovesNL/glow.git"
 repository = "https://github.com/grovesNL/glow"
-license = "MIT OR Apache-2.0"
+license = "MIT OR Apache-2.0 OR Zlib"
 edition = "2018"
 
 [package.metadata.docs.rs]

LICENSE-ZLIB

@@ -0,0 +1,15 @@
+This software is provided 'as-is', without any express or implied
+warranty.  In no event will the authors be held liable for any damages
+arising from the use of this software.
+
+Permission is granted to anyone to use this software for any purpose,
+including commercial applications, and to alter it and redistribute it
+freely, subject to the following restrictions:
+
+1. The origin of this software must not be misrepresented; you must not
+   claim that you wrote the original software. If you use this software
+   in a product, an acknowledgment in the product documentation would be
+   appreciated but is not required.
+2. Altered source versions must be plainly marked as such, and must not be
+   misrepresented as being the original software.
+3. This notice may not be removed or altered from any source distribution.

README.md

@@ -24,8 +24,9 @@ cargo build --target wasm32-unknown-unknown
 
 ## License
 
-This project is licensed under either of [Apache License, Version
-2.0](LICENSE-APACHE) or [MIT license](LICENSE-MIT), at your option.
+This project is licensed under any one of [Apache License, Version
+2.0](LICENSE-APACHE), [zlib License](LICENSE-ZLIB), or [MIT
+license](LICENSE-MIT), at your option.
 
 ## Contribution