Add ProducerOf.apply2/ConsumerOf.apply2 for binary compatibility [CE2]

[Z1kkurat]

This is a continuation of #373 and a back-port of #376

[coveralls]

Pull Request Test Coverage Report for Build 5964648481

• 0 of 2 (0.0%) changed or added relevant lines in 2 files are covered.
• 4 unchanged lines in 3 files lost coverage.
• Overall coverage decreased (-0.3%) to 75.566%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
skafka/src/main/scala/com/evolutiongaming/skafka/consumer/ConsumerOf.scala	0	1	0.0%
skafka/src/main/scala/com/evolutiongaming/skafka/producer/ProducerOf.scala	0	1	0.0%

Files with Coverage Reduction	New Missed Lines	%
skafka/src/main/scala/com/evolutiongaming/skafka/consumer/Consumer.scala	1	57.71%
skafka/src/main/scala/com/evolutiongaming/skafka/Converters.scala	1	90.91%
skafka/src/main/scala/com/evolutiongaming/skafka/producer/ProducerConfig.scala	2	91.03%

Totals
Change from base Build 5964245748:	-0.3%
Covered Lines:	1268
Relevant Lines:	1678

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💛 - Coveralls