Added get_lg_k to cpc's python wrapper

[tadejstajner]

We're using the CPC module from Python, and it's convenient to be able to call get_lg_k to see with what parameter a sketch was configured with. This PR exposes it via Python bindings.

[coveralls]

Pull Request Test Coverage Report for Build 5312561750

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 97.012%

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Totals
Change from base Build 5258088741:	0.0%
Covered Lines:	4902
Relevant Lines:	5053

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💛 - Coveralls