Fixed overly general exception in Python code.

Pylint discovered that I was raising Exception,
which was overly general. I didn't mean to do that;
it was supposed to be my custom exception type
astronomy.Error instead. So I fixed that case.

There were also some deprecated settings in the
pylint configuration file, so I fixed those too.

source/python/astronomy/astronomy.py

@@ -6955,7 +6955,7 @@ def SphereFromVector(vector):
     dist = math.sqrt(xyproj + vector.z*vector.z)
     if xyproj == 0.0:
         if vector.z == 0.0:
-            raise Exception('Zero-length vector not allowed.')
+            raise Error('Zero-length vector not allowed.')
         lon = 0.0
         if vector.z < 0.0:
             lat = -90.0