(zilch planner): initialize build planner

This provides the core for a persistent unified build plan format.

planner/default.nix

@@ -0,0 +1,11 @@
+{ chickenPackages, callPackage }:
+(callPackage ../lib/build-chicken-parallel {}) {
+  name = "zilch-planner";
+  src = ./.;
+
+  buildInputs = with chickenPackages.chickenEggs; [
+    chickenPackages.chicken
+    r7rs
+    srfi-146
+  ];
+}