CreateCursor, valueMask and format

Hello !

Here is all I did to make this lib works as I expected.
There is more tests that pass here now :p

Feel free to comment, criticize and discuss !

Ps: Some format you gave for configureWindow were strange (like 'ssx' or 'Cxxx' , maybe a typo error ?)
Also, why do you add these 'xx' everywhere ? 
I would do:

```
should.not.exist(err);
xtest = ext;
done();