Add typescript support

[piotrekwitkowski]

Issue #20

Description of changes:

• installed typescript dependency, added tsconfig.json
• moved index.js to src/index.ts, changed imports to typescript-style and fixed ts compiler errors
• added typings information to package.json
• adjusted eslint to work with typescript source and made sure there are no linting warnings or errors
• adjusted jest to be able to parse ts file in the new location and made sure all tests pass

Other things to be considered:

• with the current tsc configuration the js file will be generated in the dist folder and will not be available (like before - ready to use in the js format) in the project's root. I added dist to .gitignore, but if the previous behavior is desired, the tsconfig.json and package.json can of course be modified to reflect this

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[pedromgarcia]

Hi @piotrekwitkowski,

Thanks for submitting this PR, everything looks good so we will merge the changes and publish a new version.

[pedromgarcia]

Resolving #20