Add missing keywords, update API in README

Author: FokkeZB

README.md

@@ -25,12 +25,14 @@ TheThingsNetwork class features the following [public methods](https://github.co
 
 ```C++
   public:
+    int downlinkPort;
+    byte downlink[64];
     void init(Stream& modemStream, Stream& debugStream);
     void reset(bool adr = true, int sf = DEFAULT_SF, int fsb = DEFAULT_FSB);
     bool personalize(const byte devAddr[4], const byte nwkSKey[16], const byte appSKey[16]);
     bool join(const byte appEui[8], const byte appKey[16]);
-    void sendBytes(const byte* buffer, int length, int port = 1, bool confirm = false);
-    void sendString(String message, int port = 1, bool confirm = false);
+    int sendBytes(const byte* buffer, int length, int port = 1, bool confirm = false);
+    int sendString(String message, int port = 1, bool confirm = false);
     void showStatus();
 ```
 

keywords.txt

@@ -12,6 +12,15 @@ TheThingsNetwork       	KEYWORD1
 # Methods and Functions (KEYWORD2)
 #######################################
 
+debugPrintLn			KEYWORD2
+debugPrintLn			KEYWORD2
+
+HEX_CHAR_TO_NIBBLE		KEYWORD2
+HEX_PAIR_TO_BYTE		KEYWORD2
+
+downlinkPort			KEYWORD2
+downlink				KEYWORD2
+
 init					KEYWORD2
 reset					KEYWORD2
 personalize				KEYWORD2
@@ -20,9 +29,6 @@ sendBytes				KEYWORD2
 sendString				KEYWORD2
 showStatus				KEYWORD2
 
-debugPrintLn			KEYWORD2
-debugPrintLn			KEYWORD2
-
 #######################################
 # Constants (LITERAL1)
 #######################################
@@ -31,5 +37,7 @@ DEFAULT_WAIT_TIME		LITERAL1
 DEFAULT_FSB				LITERAL1
 DEFAULT_FSB				LITERAL1
 
+ADR_SUPPORTED			LITERAL1
+
 PWRIDX_868           	LITERAL1
 PWRIDX_915				LITERAL1