Update README file.
Initial Account model implementation

Provides means through which an account is authenticated and reasons for
which an account may fail to authenticate.

After many failed login attempts the account is locked for two hours and
unlocked after the lock is expired.

A gravatar may be retrieved from an account document by reading its
`gravatar` property.

Passwords are encrypted using a `sha-256` algorithm with hex encoding.
Create `package.json` file

File describes application dependencies. The `node_modules` directory was
added to Git ignored list.
Update account model forgot username and password static methods.
Create unit test for Account model