peepmatic: Introduce the peepmatic-macro crate

This crate provides the derive macros used by `peepmatic`, notable AST-related
derives that enumerate child AST nodes, and operator-related derives that
provide helpers for type checking.

cranelift/peepmatic/crates/macro/Cargo.toml

@@ -0,0 +1,15 @@
+[package]
+name = "peepmatic-macro"
+version = "0.1.0"
+authors = ["Nick Fitzgerald <fitzgen@gmail.com>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+proc-macro2 = "1.0.9"
+quote = "1.0.3"
+syn = { version = "1.0.16", features = ['extra-traits'] }
+
+[lib]
+proc_macro = true