Fixed style issues and build for clang-7;
64-bit buffer for BitReader and BitWriter;
Fixed overflow and writing more bytes on flushing;
Added maskLowBits() and tests for it.
* BitHelpers.cpp was removed, corresponding code was moved to the header
* BitIO test as GTest-based test binary
* gtest-based unit test for DoubleDelta and Gorilla codecs
* getLeadingZeroBits from SFINAE to consexpr if
* removed couple of unneeded if's
* Fixed sql-test to use one table
Added DoubleDelta column encoding + test cases;
Added BitWriter and BitReader that allow to read data from ReadBuffer
and write data to WriteBuffer bit by bit, up to 64 bits at once;
Added test for BitReader and BitWriter.
