add support to include_sass macro to autocompile sass files and include it in the binaries

[prabirshrestha]

Most of the template engines doesn't support css/sass files. Would be great if there was include_sass_str!("./style.sass") and include_sass_bytes!("./sytle.sass") so that we can easily embed the compiled version of the file without creating a build.rs file.

Looking to something similar to this https://crates.io/crates/include-flate.