Dictionaries ddl parser

Serialize Null Fields correctly in DataTypeNullable.

Make sure dh_clean not touch potential source files.

added groupBitmapAnd, groupBitmapOr, groupBitmapXor

Include Field.h and FieldVisitor.h into fewer files.

Lazy Database

Fix uniqCombined() result for >UINT_MAX values (return UInt64 to avoid overflow)

Merging "Optimize empty IN subquery and empty INNER/RIGHT JOIN"

Accept multiple test filter arguments in clickhouse-test.

Sometimes it is more convenient to supply space-separated test names
without having to concatenate them into one regex with pipes.

* Update index.md

translate the index.md

* Update distinctive_features.md

modify the data compression description

* Update distinctive_features.md

修改 多核心并行处理 章节

* Update distinctive_features.md

* continue to complete pr from lvxin1986

* continue to complete pr from lvxin1986

uniqCombined() return type is UInt64, but uniqCombined() uses
CombinedCardinalityEstimator, and CombinedCardinalityEstimator::size()
return type is UInt32, while the underlying HyperLogLog::size() is
UInt64.

So after this patch uniqCombined() can be used for >UINT_MAX values, the
outcome is not ideal (#2073) but at least sane.