Implement ThreadSafeFunction class

This PR is implementing ThreadSafeFunction class wraps
napi_threadsafe_function features.

FYI, the test files that included in this PR have come from Node.js
repo[1]. They've been rewritten based on C++ and node-addon-api.

[1] https://github.com/nodejs/node/tree/e800f9d/test/node-api/test_threadsafe_function

PR-URL: #442
Fixes: #312
Reviewed-By: Michael Dawson <[email protected]>
Reviewed-By: Gabriel Schulhof <[email protected]>

Author: romandev