Issue 29 Network State

This pull request addresses issue #29 Provide the Current Network State. 

Just adds two methods into Merlin class which will retrieve the network info from a given context and return the network status. 

~~I was tempted to create a dummy Application in the android manifest and have it static so that you would not be required to pass a context in order to retrieve a network status, but there wouldn't be any guarantee that the onCreate would be called before someone tried to access the isConnected method.~~

^^ Me forgetting that this is a library :tongue: 


so in `com.novoda.merlin` there should be only two classes that are public - making searching easy - explanatory javadoc helps this.

it can be an internal connectivity helper, but the beard is the public facing api. it can just wrap an internal class if you want it moved.

Yes beard means nothing but it just differentiates this class (which is a simple helper) vs the other class which you need to register a listener for.

If you had `Merlin.Builder().build() and Merlin.beard()` THAT would be confusing right?

or even more sensible
```
Merlin.Builder().withBlah().build(this);
Merlin.from(this).isConnected();
```
However looking at `Merlin` That would mean you could actually do
`new Merlin().bind().isConnected();` 
which wouldn't work and would break, to avoid this you'd need to return a different type from `Merlin.from(this)` (which could be `MerlinsBeard`), but then why even have the `Merlin.from` entry point, as we discussed above have two on the same class is confusing. Might as well split them to start with.
`Merlin.Builder().build(this)`
`MerlinsBeard.from(this)`

ALTERNATIVELY if you wanted one entry point of `Merlin` you would need to mirror the `Builder()` with a `Beard()`
but that is confusing because you have two entry points on one class.

All the above (to me) feels like two separate classes eases a lot of issues and a lot of questions.

1 class for the full Merlin implementation with constant callbacks

Another class for a give me the state right now then be gone