restructure + parser + readme updates

backends/backend.cpp

@@ -0,0 +1,6 @@
+#include "../http.cpp"
+
+class backend {
+public:
+  virtual http_response handle_request(http_request req) {};
+};

backends/file_backend.cpp

@@ -0,0 +1,21 @@
+#include "backend.cpp"
+
+class file_backend : public backend {
+public:
+  http_response handle_request(http_request req) {
+     string filename = req.path() == "/" ? "index.html" : req.path();
+     filename = "./www/" + filename;
+     ifstream stream(filename);
+
+     int status = 200;
+     if (!stream.is_open()) {
+         status = 404;
+         filename = "./error_pages/404.html";
+         stream = ifstream(filename);
+     }
+
+     stringstream buffer;
+     buffer << stream.rdbuf();
+     return http_response(buffer.str(), status);
+  }
+};