Release new Version

[hakkelt]

May I register version 0.4.0?
@nantonel @lostella

[lostella]

Sounds good to me!

[hakkelt]

Version 0.4.0 has been released, and I'm currently working on releasing sub-packages (DPSOperators, FFTWOperators, etc). This is blocked by missing license files in sub-packages. It is to be fixed in #33