specify hashability
Document, that the node objects need to be hashable.
If there is more required, then feel free to add this in this PR.
Coverage increased (+1.05%) to 94.382% when pulling 7ecd48e7b9ff578e94533d756dd771c802dcc171 on kopp:feature/specify-hashability into c4cc558a48f07efe78b8ef2cefa3cec98e0d63d0 on jrialland:master.
Coverage remained the same at 93.103% when pulling d4d28ba29b9be9e0e5db2b0c8fea8d87ca93328b on kopp:feature/specify-hashability into 642dd4bcef9829776614dc0f12681ac94634a3bc on jrialland:master.
I will have to expand on my explanation of dayaclass, I guess -- mention frozen and astuple and other built in types. Let me try to do that before you merge.