fix issue #2 callback hell

[FerrariAndrea]

• Rework callback to promise (async/await) finished and tested.
• WARN: some fixes are due to resolve other issues
• Removed some useless files
• Jest coverage: 95.27%
• Jest test passed, still 1 test failed cause of Zion query parser

Closes #2

[relu91]

There are some changes in the package.json and package-lock.json that seems related to #10, can you remove unrelated changes?

[FerrariAndrea]

Pls have a look on that, is ok now?

[relu91]

Let's move on :)