Break up library into macros and map nested libraries for shared dependency with constant map macro.

macros/Cargo.toml

@@ -0,0 +1,16 @@
+[package]
+name = "macros"
+version = "0.0.0"
+authors = ["paladin <christian.lincoln25@ic.ac.uk>"]
+description = "Procedural macros for Deimos"
+keywords = ["template", "proc_macro", "procmacro"]
+edition = "2018"
+
+[lib]
+proc-macro = true
+
+[dependencies]
+quote = "1"
+proc-macro2 = "1.0"
+syn = "1.0"
+map = { path = "../map" }

macros/src/lib.rs

@@ -0,0 +1,19 @@
+extern crate proc_macro;
+use proc_macro::TokenStream;
+
+use syn::{parse_macro_input, DeriveInput};
+use quote::quote;
+
+/// Example of [function-like procedural macro][1].
+///
+/// [1]: https://doc.rust-lang.org/reference/procedural-macros.html#function-like-procedural-macros
+#[proc_macro]
+pub fn map(input: TokenStream) -> TokenStream {
+    let input = parse_macro_input!(input as DeriveInput);
+
+    let tokens = quote! {
+        const 
+    };
+
+    tokens.into()
+}