Add support for Android 2.3+

There have been plenty of ppl involved in creating this version.
I don't wanna mention names as I'm sure I'd forget someone so I
just tell where help has been done:
- The partial android versions done by various ppl
- Testing on different android devices
- reviewing code (especially the in core changes)
- testing controls
- reviewing texts

A big thank you to everyone helping this to be completed!

src/touchscreengui.h

@@ -0,0 +1,160 @@
+/*
+Copyright (C) 2014 sapier
+
+This program 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 program 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 program; if not, write to the Free Software Foundation, Inc.,
+51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+*/
+
+#ifndef TOUCHSCREENGUI_HEADER
+#define TOUCHSCREENGUI_HEADER
+
+#include <IGUIEnvironment.h>
+#include <IGUIButton.h>
+#include <IEventReceiver.h>
+
+#include <vector>
+#include <map>
+
+#include "game.h"
+#include "tile.h"
+
+using namespace irr;
+using namespace irr::core;
+using namespace irr::gui;
+
+typedef enum {
+	forward_id = 0,
+	backward_id,
+	left_id,
+	right_id,
+	jump_id,
+	crunch_id,
+	inventory_id,
+	chat_id,
+	after_last_element_id
+} touch_gui_button_id;
+
+#define MIN_DIG_TIME_MS 500
+#define MAX_TOUCH_COUNT 64
+
+extern const char** touchgui_button_imagenames;
+
+class TouchScreenGUI
+{
+public:
+	TouchScreenGUI(IrrlichtDevice *device, IEventReceiver* receiver);
+	~TouchScreenGUI();
+
+	void translateEvent(const SEvent &event);
+
+	void init(ISimpleTextureSource* tsrc,float density);
+
+	double getYaw() { return m_camera_yaw; }
+	double getPitch() { return m_camera_pitch; }
+	line3d<f32> getShootline() { return m_shootline; }
+
+	void step(float dtime);
+	void resetHud();
+	void registerHudItem(int index, const rect<s32> &rect);
+	void Toggle(bool visible);
+
+	void Hide();
+	void Show();
+
+private:
+	IrrlichtDevice*         m_device;
+	IGUIEnvironment*        m_guienv;
+	IEventReceiver*         m_receiver;
+	ISimpleTextureSource*   m_texturesource;
+	v2u32                   m_screensize;
+	std::map<int,rect<s32> > m_hud_rects;
+	std::map<int,irr::EKEY_CODE> m_hud_ids;
+	bool                    m_visible; // is the gui visible
+
+	/* value in degree */
+	double                  m_camera_yaw;
+	double                  m_camera_pitch;
+
+	line3d<f32>             m_shootline;
+
+	rect<s32>               m_control_pad_rect;
+
+	int                     m_move_id;
+	bool                    m_move_has_really_moved;
+	s32                     m_move_downtime;
+	bool                    m_move_sent_as_mouse_event;
+	v2s32                   m_move_downlocation;
+
+	struct button_info {
+		float            repeatcounter;
+		irr::EKEY_CODE   keycode;
+		std::vector<int> ids;
+		IGUIButton*      guibutton;
+		bool             immediate_release;
+	};
+
+	button_info m_buttons[after_last_element_id];
+
+	/* gui button detection */
+	touch_gui_button_id getButtonID(s32 x, s32 y);
+
+	/* gui button by eventID */
+	touch_gui_button_id getButtonID(int eventID);
+
+	/* check if a button has changed */
+	void handleChangedButton(const SEvent &event);
+
+	/* initialize a button */
+	void initButton(touch_gui_button_id id, rect<s32> button_rect,
+			std::wstring caption, bool immediate_release );
+
+	/* load texture */
+	void loadButtonTexture(button_info* btn, const char* path);
+
+	struct id_status{
+		int id;
+		int X;
+		int Y;
+	};
+
+	/* vector to store known ids and their initial touch positions*/
+	std::vector<id_status> m_known_ids;
+
+	/* handle a button event */
+	void ButtonEvent(touch_gui_button_id bID, int eventID, bool action);
+
+	/* handle pressed hud buttons */
+	bool isHUDButton(const SEvent &event);
+
+	/* handle released hud buttons */
+	bool isReleaseHUDButton(int eventID);
+
+	/* handle double taps */
+	bool doubleTapDetection();
+
+	/* doubleclick detection variables */
+	struct key_event {
+		unsigned int down_time;
+		s32 x;
+		s32 y;
+	};
+
+	/* array for saving last known position of a pointer */
+	v2s32 m_pointerpos[MAX_TOUCH_COUNT];
+
+	/* array for doubletap detection */
+	key_event m_key_events[2];
+};
+extern TouchScreenGUI *g_touchscreengui;
+#endif