V1.7.0 checklist

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• review Async in method names; consider removing in line with modern APIs #47
• ~probably remove validateBrokerUri as its no longer an integral part of the API as of 1.4~ in 1.5
• ~prune less frequently used arguments in Create calls~ in 1.5.6
• [x] Complete #86 @deviousasti
• [x] remove FsKafka0 https://github.com/jet/FsKafka/commit/eed99405ceadc0d9a12665b025d57d6585081dea
• [x] remove net461 multi-targeting
• [x] remove https://github.com/jet/FsKafka/blob/f4391539679441913b56a879e6638fe257df3d5a/src/FsKafka/FsKafka.fs#L222
• [x] target CK 1.7.0

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@deviousasti As discussed in #86, we should do the right thing for FsKafka0 now. This would also enable Propulsion 2.11.0 (which should more correctly be named 3.0.0 based on the work list in https://github.com/jet/propulsion/issues/116)