Generalise support for dynamic shadowing in dxtbx about dxtbx HOT 1 OPEN

Two additions to the description above:

• We must handle the case where the shadowing object's rotation does not match that of the sample. For example, we must account for the movement of the κ arm of a mini-κ goniometer. The specification should therefore include the axis on which the object is mounted.
• We must allow for objects with multiple apertures, such as the forward and backward apertures of a diamond anvil cell, in which case valid = allowed_1 | allowed_2. So the specification must permit distinction between & and | combination.

from dxtbx.