Define RAPIDJSON_HAS_CXX11_RVALUE_REFS directly in clang

This makes no difference except that it avoids "warning: macro expansion
producing 'defined' has undefined behavior" messages.

Add filterkey and filterkeydom examples

Also disable copy constructor/assignment operator

Adding spaces in Chinese doc

Try to fix cmake CMP0054 warning

Fix #606

Fix schema "required" keyword cannot handle duplicated keys

Fix #608

Fix regex crash

Due to dereferencing a pointer which may be invalidated

Improve coverage to 100%