core: Implement basic git integration

Missing streaming, so git's a bit confused, but works.

Also easy to bypass. Although I doubt any mf at alibaba gon bypass it
with his custom UA.

src/config/Config.hpp

@@ -13,6 +13,7 @@ class CConfig {
         std::string       data_dir         = "";
         std::string       html_dir         = "";
         unsigned long int max_request_size = 10000000; // 10MB
+        bool              git_host         = false;
     } m_config;
 };