Add String::concat(const uint8_t *, unsigned int) version

This just calls the char* version, but allows calling the method with a
uint8_t* as well (which is not uncommon for buffers).

Author: matthijskooijman

Diff for: api/String.h

@@ -111,6 +111,7 @@ class String
 	unsigned char concat(const String &str);
 	unsigned char concat(const char *cstr);
 	unsigned char concat(const char *cstr, unsigned int length);
+	unsigned char concat(const uint8_t *cstr, unsigned int length) {return concat((const char*)cstr, length);}
 	unsigned char concat(char c);
 	unsigned char concat(unsigned char num);
 	unsigned char concat(int num);