move jpeg encoding to a worker thread pool

this also switches cvmts back to building with tsc, mostly because
I couldn't get parcel's worker interop to work at all.

cvmts/tsconfig.json

@@ -1 +0,0 @@
-../tsconfig.json

cvmts/tsconfig.json

@@ -0,0 +1,7 @@
+{
+  "extends": "../tsconfig.json",
+  "include": [ "src/**/*" ], 
+  "compilerOptions": {
+    "resolveJsonModule": true,
+  }
+}