Basic support for esp8266 platform

This includes empty stubs for most core Arduino functions.
Need to actually implement all those digital reads writes whatever.
Need to prebuild toolchains (xtensa-elf-lx106) for 3 platforms and put them on some download server.
Need to do the same with esptool.
Need to fix 0x40000 binary generation and add correct upload commands.
Maybe even implement uploads over WiFi.

cores/esp8266/Tone.cpp

@@ -0,0 +1,49 @@
+/* Tone.cpp
+
+  A Tone Generator Library
+
+  Written by Brett Hagman
+
+  This library is free software; you can redistribute it and/or
+  modify it under the terms of the GNU Lesser General Public
+  License as published by the Free Software Foundation; either
+  version 2.1 of the License, or (at your option) any later version.
+
+  This library is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public
+  License along with this library; if not, write to the Free Software
+  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+
+Version Modified By Date     Comments
+------- ----------- -------- --------
+0001    B Hagman    09/08/02 Initial coding
+0002    B Hagman    09/08/18 Multiple pins
+0003    B Hagman    09/08/18 Moved initialization from constructor to begin()
+0004    B Hagman    09/09/26 Fixed problems with ATmega8
+0005    B Hagman    09/11/23 Scanned prescalars for best fit on 8 bit timers
+                    09/11/25 Changed pin toggle method to XOR
+                    09/11/25 Fixed timer0 from being excluded
+0006    D Mellis    09/12/29 Replaced objects with functions
+0007    M Sproul    10/08/29 Changed #ifdefs from cpu to register
+0008    S Kanemoto  12/06/22 Fixed for Leonardo by @maris_HY
+*************************************************/
+
+#include "Arduino.h"
+#include "pins_arduino.h"
+
+
+static int8_t toneBegin(uint8_t _pin)
+{
+}
+
+void tone(uint8_t _pin, unsigned int frequency, unsigned long duration)
+{
+}
+
+void noTone(uint8_t _pin)
+{
+}