RPi: Improve build process

Add option to set an external arduino libraries directory.
All libraries from this folder will be compile and available for use
in the gateway.
Some Arduino libraries can be used on Linux/RPI with minor adjustments,
but there are some that will have to be completely rewritten.

The build process uses a separate folder for objects and binary files
which can be set by the user.

Initialize the bcm2835 inside a class constructor to fix cases where
pin operations are used before hwInit().

Fix SPI pins default values.

Fix activation interrupt functions.

Fix some headers.

Rename gateway binary and services to mysgw.

examples_linux/mysgw.cpp

@@ -5,8 +5,8 @@
  * repeater and gateway builds a routing tables in EEPROM which keeps track of the
  * network topology allowing messages to be routed to nodes.
  *
- * Created by Marcelo Aquino <marceloaqno@gmail.org>
- * Copyleft (c) 2016, Marcelo Aquino
+ * Created by Henrik Ekblad <henrik.ekblad@mysensors.org>
+ * Copyright (C) 2013-2016 Sensnology AB
  * Full contributor list: https://github.com/mysensors/Arduino/graphs/contributors
  *
  * Documentation: http://www.mysensors.org
@@ -67,15 +67,25 @@
 // Note: MY_SIGNING_REQUEST_SIGNATURES must also be set
 //#define MY_SIGNING_GW_REQUEST_SIGNATURES_FROM_ALL
 
+// Enables RF24 encryption (all nodes and gateway must have this enabled, and all must be
+// personalized with the same AES key)
+//#define MY_RF24_ENABLE_ENCRYPTION
+
 #include <MySensors.h>
 
-void setup() { 
+#define ARDUINO 100
+// This space is intended to be used to include arduino libraries
+
+#undef ARDUINO
+
+void setup() {
+	// Setup locally attached sensors
 }
 
 void presentation() {
-  // Present locally attached sensors here    
+	// Present locally attached sensors here    
 }
 
 void loop() {
-  // Send locally attached sensors data here
+	// Send locally attached sensors data here
 }