Move to PROGMEM aware libc, allow PSTR in printf()

cores/esp8266/Arduino.h

@@ -253,7 +253,7 @@ const int TIM_DIV265 __attribute__((deprecated, weak)) = TIM_DIV256;
 #ifdef __cplusplus
 
 #include <algorithm>
-#include "pgmspace.h"
+#include <pgmspace.h>
 
 #include "WCharacter.h"
 #include "WString.h"

cores/esp8266/libc_replacements.c

@@ -128,4 +128,4 @@ void _exit(int status) {
 int atexit(void (*func)()) {
     (void) func;
     return 0;
-}
+}