Do proper typetesting for np.floats

[JoranAngevaare]

What is the problem / what does the code in this PR do
Solves issue: #326

Can you briefly describe how it works?
See:
https://stackoverflow.com/questions/28292542/how-to-check-if-a-number-is-a-np-float64-or-np-float32-or-np-float16

Can you give a minimal working example (or illustrate with a figure)?

d = np.float32(1)
isinstance(d, np.float), isinstance(d, np.floating)
# returns
(False, True)

[WenzDaniel]

Nice catch