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"))
```
For the sake of being symmetric.. I have also added `Func<string, bool> OnlyIncludeScripts(params string[] scriptNames)` - that ok?