Added Default Script Name Conventions.

See #69.
The test will fail when fixing the bug.
Changing the filesystem setup to

```csharp
fixture.FileSystem.GetFile(Arg.Is<FilePath>(fp => fp.FullPath == scriptName))
    .Returns(new FakeFile(new FakeFileSystem(false), 
        new FilePath(scriptName)) { Exists = true});
```

Will fix the test.