Add support for building organic via nix.

nix/package.nix

@@ -0,0 +1,75 @@
+{
+  hello,
+  lib,
+  makeRustPlatform,
+  pkgsBuildHost,
+
+  targetBins ? [ ],
+  features ? [ ],
+  cargoBuildTarget ? null,
+  buildType ? null,
+  buildLib ? false,
+}:
+let
+  cargoToml = (lib.importTOML ../Cargo.toml);
+  rustToolchain = (pkgsBuildHost.rust-bin.fromRustupToolchainFile ../rust-toolchain.toml).override (
+    if cargoBuildTarget != null then
+      {
+        targets = [ cargoBuildTarget ];
+      }
+    else
+      { }
+  );
+  baseRustPlatform = (
+    makeRustPlatform {
+      cargo = rustToolchain;
+      rustc = rustToolchain;
+    }
+  );
+  rustPlatform =
+    if cargoBuildTarget != null then
+      baseRustPlatform.overrideScope (
+        final: prev: {
+          cargoBuildHook = prev.cargoBuildHook.overrideDerivation (_: {
+            rustcTargetSpec = cargoBuildTarget;
+          });
+          cargoInstallHook = hello;
+        }
+      )
+    else
+      baseRustPlatform;
+in
+rustPlatform.buildRustPackage (
+  {
+    pname = "organic";
+    version = cargoToml.package.version;
+    src = lib.cleanSource ../.;
+
+    cargoLock.lockFile = ../Cargo.lock;
+
+    cargoBuildFlags = builtins.concatLists [
+      (builtins.concatMap (targetBin: [
+        "--bin"
+        targetBin
+      ]) targetBins)
+      (if buildLib then [ "--lib" ] else [ ])
+      (
+        if features != [ ] then
+          [
+            "--features"
+            (builtins.concatStringsSep " " features)
+          ]
+        else
+          [ ]
+      )
+    ];
+  }
+  // (
+    if buildType != null then
+      {
+        buildType = buildType;
+      }
+    else
+      { }
+  )
+)