Filtering Scripts

This is the FilterFactory implementation with Unit Tests as I have proposed for #54 

Usage of the FilterFactory class would be:

```csharp
.WithScriptsEmbeddedInAssembly(Assembly.GetExecutingAssembly(),
 FilterFactory.ExcludeScriptNamesInFile("scriptnames.txt"))
```
I think we need to add xml comments on here, saying one script per line in the file etc.