Convert project to TypeScript

[paceaux]

Project should be in TS b/c that would be easier for documentation.

[paceaux]

Branch created: https://github.com/paceaux/methodius/tree/issue18-convert-to-ts

[paceaux]

How to test this

1: Create a test project (e.g. methodius-test)

put this in an index.js file:

const Methodius = require('methodius');
const test = new Methodius('Hey there frank. How is it going? Is there anything you would like to do? I am wondering what happens here. I am excited. This should be fun.');

const ngrams = test.bigrams;

console.log(ngrams);
console.log(test.trigrams);

2. Add this to the scripts for the project's package.json

   
   "scripts": {
   "test": "node index.js"
   }

3. In the Methodius package, set it as a link:
```Bash
npm link

4. In the test package, tell it to use your local package:

 npm unlink methodius && npm link methodius && npm run test

Expected result:

console.log runs without error.

[paceaux]

This runs without error. It was a lot of effort. Got released in 2.0.0 last night. Someone please clap.

:clap: