Replace shared_ptr with unique_ptr for better performance (#695)
Replace shared_ptr with unique_ptr for better performance (#695)

* Backport std::make_unique from C++14.

* Replace shared_ptr with unique_ptr for better performance.

Co-authored-by: Ella <15400a712d11901ac2296ecf832bec4f3e30b7d2@otcaix.iscas.ac.cn>
yhirose/cpp-httplib,yhirose/cpp-httplib,yhirose/cpp-httplib,yhirose/cpp-httplib