Add code coverage command

.gitignore

@@ -1,2 +1,4 @@
 .DS_Store
-node_modules/
+node_modules/
+coverage
+.vscode

package.json

@@ -9,7 +9,8 @@
   },
   "scripts": {
     "format": "find . -name '*.js*' | xargs prettier --write --config ./.prettierrc --config-precedence file-override",
-    "test": "jest"
+    "test": "jest",
+    "test:coverage": "jest --coverage"
   },
   "keywords": [
     "monero",
@@ -35,5 +36,12 @@
   },
   "devDependencies": {
     "jest": "^23.1.0"
+  },
+  "jest" : {
+    "coveragePathIgnorePatterns": [
+      "node_modules", 
+      "cryptonote_utils/biginteger.js",
+      "cryptonote_utils/sha3.js",
+      "cryptonote_utils/cryptonote_crypto_EMSCRIPTEN.js"]
   }
 }