Filter operators rebase

[fredludlow]

Rebase of #49 on current master.

As previously commented, this is a bit of an experiment. It currently works well for me, but I'm very happy to play around with the syntax if anyone has suggestions for improvement,

[fredludlow]

ps. Travis CI (triggered by pushing to my fork rather than creating the PR) failed for python 3.3 (the typing package not compatible).

If the intention is still to support python 3.3 (not relevant for me but maybe for others) then I think typing version 3.6.6 would support 3.3 https://pypi.org/project/typing/3.6.6/

[michaelbukachi]

ps. Travis CI (triggered by pushing to my fork rather than creating the PR) failed for python 3.3 (the typing package not compatible).

If the intention is still to support python 3.3 (not relevant for me but maybe for others) then I think typing version 3.6.6 would support 3.3 https://pypi.org/project/typing/3.6.6/

Python 3.3 reached it's end-of-line 3 years ago (https://endoflife.date/python). So I think we can stop supporting it.

[PrasanthChettri]

@michaelbukachi will this be merged in the future ? seems useful

[michaelbukachi]

Hi @PrasanthChettri yes, eventually. We are still trying to see if this is the best approach to handle or/and operators. If you have any ideas on how we should handle this, post them in #47 so that we can discuss it further.

[michaelbukachi]

@fredludlow One more thing. Is this PR a breaking change? Will users be able to still use filters the same they have been doing so before?

[fredludlow]

My intention was that it wasn't going to break any existing behaviour (I added some new tests for the extended behaviour but the old tests should still all pass)

[michaelbukachi]

Awesome. Thanks.

[michaelbukachi]

I'll do a release over the weekend.