Started to implement server

vendor/import_map.json

@@ -1,6 +1,7 @@
 {
   "imports": {
     "https://denopkg.com/chiefbiiko/sha1/mod.ts": "./denopkg.com/chiefbiiko/sha1@master/mod.ts",
+    "https://deno.land/x/oak/mod.ts": "./deno.land/x/oak@v12.1.0/mod.ts",
     "https://deno.land/std/testing/asserts.ts": "./deno.land/std@0.191.0/testing/asserts.ts",
     "https://deno.land/": "./deno.land/",
     "https://denopkg.com/": "./denopkg.com/"