Use Jest for testing

[saminzadeh]

After #13 was merged, the testing will start to fail if we use more ES6 features.

This PR changes the testing framework to use Jest instead of mocha which is becoming an industry standard.

Some of it's features include:

• Babel support out of the box
• Code coverage, test watchers
• Snapshot testing, etc

A few notes:

• Moved test folder to __test__ as it works out of the box for Jest

[cigolpl]

The Jest works nice! Merging