* node-cache: return refs instead of clone for speed.
* add '--disableDbCaching' flag
* reduce heap usage by 50% (118MB -> 58.8MB via Chrome Heap Profiler) via disabling source map during build
* improve generation speed by 75% via SQL query caching

Using full-th sample app as reference, there are 108,871 SQL query calls
spread over the following query functions

* selectAtomicType()
* selectBitmapByName()
* selectDataTypeByName()
* selectEnumByName()
* selectNumberByName()
* selectStructByName()

Performance metric:
  test runner: ./src-script/gen-test-runner.js
  machine: macbook 2.6 Ghz 6-core Intel Core i7 / 32GB DDR4

  Before:
    average generation time: 42.851s

  After:
    initial cache warm up generation time: 17.699s
    average generation time: 11.766s