Add documentation to filters.py
Add documentation to filters.py

An attempt to explain some of what is going on.

AnthonyTruchet/breathe,AnthonyTruchet/breathe,kirbyfan64/breathe,AnthonyTruchet/breathe,RR2DO2/breathe,AnthonyTruchet/breathe,RR2DO2/breathe,kirbyfan64/breathe,kirbyfan64/breathe,kirbyfan64/breathe