Add a caveat lector to the readme

[ci skip]
Clarify some details about the usage

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It's 2014 now, update the copyright

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Add clarifications about support for C* 2.0

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Add performance tips to the readme

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Add a tip about using the async API

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Fix a bug in PreparedResultResponse#to_s

It didn't format bytes < 16 right.
Prepared statements now print their ID and connection metadata to the log