fix redis cmd_format bug in the empty string case

change butil/third_party/rapidjson namespace to make it ABI-compatible with other versions of rapidjson used in the same project.

a single binary has two different rapidjson version.

add consul naming service

Improve cmake

Compile gtest as a subproject which is recommended and add a utility for downloading and building gtest source code

添加wrr的文档说明

include wrr in register_lb.png

add weighted round robin

增加wrr的说明

Rephrase automatic comments

to enable probot to close issues automatically.