Macro csp_hashes

macro_rules! csp_hashes {
    ($file_name:literal, $tag_name:literal) => { ... };
}

Include a list of allowed style hashes for use in the CSP header as a &'static str.

The hashes are in the CSP header format (sha256-HASH_ONE sha256-HASH_TWO ...), and are generated at compile time by the build script per HTML file.