Adding 'partial' prefix for class / interface generation

[kbalint]

Hello, I had to modify the generator to let all classes / interfaces have a 'partial' declaration - this way I can re-generate my whole repository and retain all the changes too - in separate files.

[OmarElabd]

Hi @kbalint, yea that's a good idea. if you'd like you can submit a pull request with the partial modifier.

related to #4