High level shape equality testing

[jdegenstein]

Currently, high level shape equality testing is not possible in build123d:

a = Box(3,2,1)
b = Box(3,2,1)
a == b # returns False

Here is my proposal to achieve the higher level __eq__:

1. Fix shape serialization bug (via patch to OCP or with ocp-addons)
2. Generate serialization of shape via BinTools (see persistence.py in build123d)
3. Hash this serialization
4. a==b compares the hashes of the serialization

@snoyer noted that step 3 may be unnecessary and it may be better to simply compare the shape serializations. It is definitely worth investigating both approaches.

This is related to, but not the same as -- lower level equality testing to wrap TopoDS_Shape.IsEqual for the purposes of comparing equality of underlying OCP shapes:
CadQuery/OCP#161