MAINT: remove deprecated calls to np.int/float

@arianna.renzini I noticed that the tests are all failing because we use the now removed np.int and np.float.

I also noticed a few other issues at the same time. The most major one was that there was a call to eval, which is generally not a good idea, especially on user inputs as it is quite easy to add a rm -rf * that will happily be evaluated and destroy the computer. I assume the reason for that was to handle inputs like 2 / 3, the new version should be fine with that.