Add Print::write(const char *, size_t)

The new function just calls Print::write(const uint8_t *, size_t), but
this allows writing out a buffer of chars (without having to learn about
casts).

cores/arduino/Print.h

@@ -51,6 +51,9 @@ class Print
       return write((const uint8_t *)str, strlen(str));
     }
     virtual size_t write(const uint8_t *buffer, size_t size);
+    size_t write(const char *buffer, size_t size) {
+      return write((const uint8_t *)buffer, size);
+    }
 
     size_t print(const __FlashStringHelper *);
     size_t print(const String &);