[PUSB] Fix static initialization order fiasco

For details see:
https://isocpp.org/wiki/faq/ctors#static-init-order-on-first-use

Author: facchinm

src/Keyboard.cpp

@@ -63,7 +63,7 @@ static const uint8_t _hidReportDescriptor[] PROGMEM = {
 Keyboard_::Keyboard_(void) 
 {
 	static HIDDescriptorListNode node(_hidReportDescriptor, sizeof(_hidReportDescriptor));
-	HID.AppendDescriptor(&node);
+	HID().AppendDescriptor(&node);
 }
 
 void Keyboard_::begin(void)
@@ -76,7 +76,7 @@ void Keyboard_::end(void)
 
 void Keyboard_::sendReport(KeyReport* keys)
 {
-	HID.SendReport(2,keys,sizeof(KeyReport));
+	HID().SendReport(2,keys,sizeof(KeyReport));
 }
 
 extern

src/Keyboard.h

@@ -94,7 +94,6 @@ class Keyboard_ : public Print
   void releaseAll(void);
 };
 extern Keyboard_ Keyboard;
-extern HID_ HID;
 
 #endif
 #endif