Make copies of input parameters

[prisae]

empymod changes some input parameters, e.g., src and rec. Example:

In [1]: from empymod import dipole 
In [2]: rec = [5000, 0, 200] 
In [3]: rec                                                                     
Out[3]: [5000, 0, 200]
In [4]: EMfield = dipole([0, 0, 200], rec, [], 1, 1, verb=0)              
In [5]: rec                                                                     
Out[5]: [array([5000.]), array([0.]), array([200.])]

Ensure that this does not happen. As this will break some code that assumed this 'behaviour', it should be put into the v2.0.0 release.

[prisae]

Just affects src and rec.