Configurable API key, Maven tweaks and Content Type

Hi,

We needed to make a few changes. First, the library didn't support a configurable API_KEY. We made API_KEY non-final and created a static apiKey(), so you can do this:

```
// do this once
Indicative.apiKey("My Key");

// do this repeatedly
Indicative.event()....;
```

We set the charset and Accept-Charset in the HTTP headers.

I also bumped the version to 1.0.1-SNAPSHOT and added the github SCM urls, this should allow you to use the maven release:prepare / release:perform cycle to make releases.

As a matter of code review, I don't mind the fluent api design, but I would prefer that Indicative.event() return an IndicativeEvent object, rather than an Indicative, which is counter intuitive. In addition, it makes it difficult to modularize the different functionality into separate classes, etc. 

Lastly, I would prefer to instantiate an Indicative object and use it as a factory service (we use Spring), which is a bit counter to the use of a static apiKey. That being said, I realize its a bit against the fluent model, so maybe thats not what you are going for.

We also considered a version where Indicative.event() took the API_KEY. You can see it in commit dce5058 (the first one). This would require us to pass the API_KEY for each event() call, but does allow the code to remain stateless, if that is what you'd prefer.