Get Phase.__str__ to work at least in basic fashion

[mhvk]

Fixes #216

Not very pretty but easiest way to work around fact that np.array2string does not allow one to override formatting of structured dtype.

[theXYZT]

What does this do? self.view(f"V{self.dtype.itemsize}")? I have never seen a "Vx" string used before in views and such.

[mhvk]

@theXYZT - it views as a "void" dtype, which stands for a pure binary blob which some number of bytes. For some reason, np.array2string allows one to override how those are represented, but not how a structured array is represented (it assumes you just want to print the individual elements of the structure).

[theXYZT]

This fails for scalar phases now, haha!

x = Phase(1.0)
str(x)

should throw an error now: AttributeError: 'numpy.void' object has no attribute 'to_string'

[mhvk]

Oops.... Fixed by #220