Remove custom heap and use bintrees

packages/0x.js/package.json

@@ -49,6 +49,7 @@
     "node": ">=6.0.0"
   },
   "devDependencies": {
+    "@types/bintrees": "^1.0.2",
     "@types/jsonschema": "^1.1.1",
     "@types/lodash": "^4.14.64",
     "@types/mocha": "^2.2.41",
@@ -87,9 +88,10 @@
     "webpack": "^3.1.0"
   },
   "dependencies": {
-    "@0xproject/assert": "0.0.3",
     "0x-json-schemas": "^0.6.1",
+    "@0xproject/assert": "0.0.3",
     "bignumber.js": "~4.1.0",
+    "bintrees": "^1.0.2",
     "compare-versions": "^3.0.1",
     "es6-promisify": "^5.0.0",
     "ethereumjs-abi": "^0.6.4",