+ Remove unnecessary loading of openssl.cnf

Update threading_overview.md

Add docs & Fix SSL UT

print bt when core dump happens in running UT

Fix unrecognizable characters in memory_management.md

为consul名字服务添加文档

Update docs for SSL

Enable SSL support for single endpoint channel

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