* Update TSConfig to produce type definitions
Also, add some stricter type-checking, and remove settings that were set
to the same value as the default for that setting.
I also reorganized the sections into the sections that TypeScript itself
generates when you boot up a `tsconfig.json` using their CLI.
* Downgrade target to ES6 for Node 8 support
* Add engines specification to package.json
Make it clear that we support Node 8 and above.
- Migrate to TypeScript and TSLint
- Vendor ripple-address-codec (move dependency into this project)
- Add support for Travis CI (.travis.yml)
- Use "dist/*" for distribution files
- Bump version to 1.0.0-beta.0
- Add yarn.lock