Convert some packages to nix-based

Affected packages:
- crystal
- dart
- dash
- deno
- elixir
- erlang
- gawk

runtimes/gawk-awk.nix

@@ -0,0 +1,26 @@
+{pkgs, piston, ...}:
+let
+    pkg = pkgs.gawk;
+in piston.mkRuntime {
+    language = "awk";
+    version = pkg.version;
+    runtime = "gawk";
+
+    aliases = [];
+
+
+    run = ''
+    ${pkg}/bin/gawk -f "$@"
+    '';
+
+    tests = [
+        (piston.mkTest {
+            files = {
+                "test.awk" = ''
+                    {print "OK"}
+                '';
+            };
+            stdin = "\n"; # awk needs some line input
+        })
+    ];
+}