Add plain char* signatures WebServer::sendContent (#6341)

Fixes #2567

Allow the web server to send plain C strings instead of requring they be
encapsulated inside a String class object.  Saves memory vs. having to
convert C strings to Strings (i.e. duplication of data), overloads on
the efficient sendContent_P(char*) methods.

Author: earlephilhower

libraries/ESP8266WebServer/src/ESP8266WebServer.h

@@ -135,6 +135,8 @@ class ESP8266WebServerTemplate
   void sendContent(const String& content);
   void sendContent_P(PGM_P content);
   void sendContent_P(PGM_P content, size_t size);
+  void sendContent(const char *content) { sendContent_P(content); }
+  void sendContent(const char *content, size_t size) { sendContent_P(content, size); }
 
   static String credentialHash(const String& username, const String& realm, const String& password);