ENH: Chain exceptions to give better error messages for invalid PEP3118 format strings

Sample console output:
```
In [1]: from ctypes import c_wchar

In [2]: x = c_wchar * 3

In [3]: np.array(x())
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
~\Repos\numeric-python\numpy\build\testenv\Lib\site-packages\numpy\core\_internal.py in _dtype_from_pep3118(spec)
    486
--> 487     dtype, align = __dtype_from_pep3118(stream, is_subdtype=False)
    488     return dtype

~\Repos\numeric-python\numpy\build\testenv\Lib\site-packages\numpy\core\_internal.py in __dtype_from_pep3118(stream, is_subdtype)
    558         else:
--> 559             raise ValueError("Unknown PEP 3118 data type specifier %r" % stream.s)
    560

ValueError: Unknown PEP 3118 data type specifier 'u'

The above exception was the direct cause of the following exception:

ValueError                                Traceback (most recent call last)
<ipython-input-3-f8a17df3aa24> in <module>()
----> 1 np.array(x())

ValueError: '<u' is not a valid PEP 3118 buffer format string
```

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