str values should be quoted in Array repr

[gdementen]

String values should be quoted in Array.__repr__. Currently, they are indistinguishable from their numeric counterpart:

>>> a = Axis('a=a0,a1')
>>> arr = Array(["1", "2"], a)
>>> arr
a  a0  a1
    1   2
>>> arr = Array([1, 2], a)
>>> arr
a  a0  a1
    1   2

The problem is even worse for object/mixed type arrays:

>>> arr = Array([1, "2"], a, dtype=object)
>>> arr
a  a0  a1
    1   2

FWIW, numpy quotes string values:

>>> arr = np.array(["1", "2"])
>>> arr
['1' '2']

I am currently undecided whether to quote string values in the editor. There you at least have the background color hint.