Add proc macros for Hint and edge (#63)

* Add proc-macro crate with two macros

* Let cargo recalculate the Cargo.lock

* Add tests and refactor some code to allow testing

also the impl for parse_hint_helper_attrs now preserves order
(which is essential for testing)

core/editor/Cargo.toml

@@ -15,3 +15,7 @@ bitflags = "1.2.1"
 [dependencies.document-core]
 path = "../document"
 package = "graphite-document-core"
+
+[dependencies.proc-macros]
+path = "../proc-macro"
+package = "graphite-proc-macros"