Add objdiff setup

This is intended more as a proof of concept as we figure things out
than the start of an actual decompilation in this repository.  Target
object files are currently "bring your own."

objdiff/objdiff.json

@@ -0,0 +1,22 @@
+{
+  "custom_make": "NMAKE.EXE",
+  "watch_patterns": [
+    "*.cpp",
+    "*.hpp"
+  ],
+  "units": [
+    {
+      "name": "Jet2",
+      "target_path": "target/Jet2.obj",
+      "base_path": "src/Jet2.obj",
+      "complete": true,
+      "metadata": {
+        "source_path": "src/Jet2.cpp"
+      },
+      "symbol_mappings": {
+        "FUN_00187710": "$L514",
+        "FUN_0018771b": "$L522"
+      }
+    }
+  ]
+}