Adding GetEpisode and GetUpdates methods

I forked this repo to complete the methods exposed on TVDB object.
Previously, only Search and GetTvShow were available.

Now, we have:
- GetEpisode; retrieve the information of a single episode
- GetUpdates; retrieve the updates (shows, episodes and banners) on thetvdb in a given time frame.

Also did a bunch of changes such as (I probably forget a bunch here...):
- Test methods in Example project
- Types of returned objects (Show Id: string -> int etc.)

Happy to discuss all those changes btw ;)