Add initial project infrastructure

[bajtos]

This pull request takes parts of #1 and makes the following changes:

• remove tsconfig.common.json, it's not needed in a single-package repo
• remove "exclude" from tsconfig, not needed
• add typescript as a dependency, configured build - slightly differently than in loopback-next, I'd like to try out a better setup
• add linting step
• add top-level index.js, src/index.ts
• add simple smoke test, configure mocha
• add VSCode project config
  • tsc-watch task + problem matcher
  • test + lint task
• explicitly list files to include in the npm package
• add DEVELOPING.md describing the dev setup
  • Node.js 8.x or newer only
  • VSCode + extensions: Prettier, tslint
  • command+shift+b to start typescript watch/build in background
  • command+shift+t to run the tests and lint the code

@virkt25 @kjdelisle PTAL

[bajtos]

connect to loopbackio/loopback-next#525

[kjdelisle]

two minor nits, otherwise LGTM

[kjdelisle]

Lost your trailing period here.

[kjdelisle]

missing newline

[bajtos]

There was an extra newline and the indentation was off too, I reformatted the code in vim.