include macros

[cjhowedev]

Write function-like procedural macros to invoke compile_hlsl and validate_dxil at compile time. I think most users of this library will want to compile their shaders to SPIR-V/DXIL at compile time because it's unlikely that players will have dxil.dll available.

To kick off the conversation, I suggest we follow in the footsteps of inline-spirv in regards to the usage patterns:

let spirv = include_hlsl!(
    "shader_filename.hlsl",
    "entry",
    "cs_6_5",
    &vec!["-spirv"],
    &vec![
        ("MY_DEFINE", Some("Value")),
        ("OTHER_DEFINE", None)
    ],
);

let dxil= validate_dxil!(inline_hlsl!(
    r#"
        // your inline HLSL code here
    "#,
    "entry",
    "cs_6_5",
    &vec![],
    &vec![
        ("MY_DEFINE", Some("Value")),
        ("OTHER_DEFINE", None)
    ],
));

I'm not sure what the API for validation should look like or whether it's feasible, but we should consider whether we will need to validate DXIL at compile time.