build: enable npm package publication from master branch

[IllusionMH]

PR checklist

• [X] Addresses an existing issue: fixes #869
• [ ] New feature, bugfix, or enhancement
  • [ ] Includes tests
• [X] Documentation update

Overview of change:

• adds files "required" for backwards compatibility
• prevents unintentional publishing from root folder
• finally updates steps for beta tags on npm 😄
• bundled tslint.json now will be created from legacy.json (therefore rules that were added after 6.0 were removed from it)

Is there anything you'd like reviewers to focus on?

After applying this PR there should be only three files inside package that differ from latest version:

1. legacy.json - removed react-a11y-accessible-headings and void-zero rules because they were added in 6.1
2. package.json - removed scripts to unblock publishing from dist/build
3. tslint.json - will produce big diff because of different formatting and rules sort. Summary of changes:
   • disabled deprecated no-reserved-keywords (recommended rule variable-name was already enabled)
   • disabled deprecated no-function-constructor-with-string-args, no-increment-decrement, and no-unnecessary-bind rules and enabled corresponding recommended rules from TSLint

[JoshuaKGoldberg]

https://travis-ci.org/microsoft/tslint-microsoft-contrib/jobs/544502075

Your build has been stopped.
Failed to download file: https://nodejs.org/dist/v6.17.1/node-v6.17.1-win-x64.7z
connect ETIMEDOUT 104.20.23.46:443

...well. Restarting.

Edit: great, it passed on rebuild. I'll hold off on merging - all you! 😊

[IllusionMH]

Verified one more time and haven't found any more differences except mentioned above changes to configuration.