Add "targets" command

src/index.ts

@@ -2,7 +2,7 @@
 
 import yargs from "yargs";
 import { hideBin } from "yargs/helpers";
-import startCompile, { Target } from "./process";
+import startCompile, { Target, Targets } from "./process";
 
 import dbg from "debug";
 const log = dbg("app");
@@ -54,6 +54,12 @@ yargs(hideBin(process.argv))
          })
       }
    )
+   .command("targets", "List all targets", (yargs)=>yargs, ()=>{
+      console.log("Targets:")
+      Targets.forEach((__dirname, target) => {
+         console.log("   " + target);
+      })
+   })
    .option("verbose", {
       alias: "v",
       type: "boolean",