Support package-private feature

[nadongguri]

I'm submitting a ...

• bug report
• feature request
• support request

General information

Prerequisites

• Are you running the latest version?

Description

It is required to use package-private feature from Java to Bacardi project even though Typescript seems not supporting this. So, I suggest

1. Adding convention rules : private starts with _, package-private starts with __
2. Adding rule for checking this in ts-lint