SHA512 password before sending to API; assert password length of 4 characters minimum

Object looks something like this now:
```js
{username: "m", password: "1fc2f0d378b1429a39359d9b46f28c595e44143e1a7f66b110…3c69cc3f58ebe01d3d992ec86ecb951117dde597145698676"}
```

resolves #14