Added love.touch module and touch screen events. Resolves issue #825.

Note: this implementation is slightly different from the implementation in the love 0.9.x Android and iOS ports!

Added love.touchpressed(id, x, y), love.touchmoved(id, x, y, dx, dy), and love.touchreleased(id, x, y, dx, dy).

id is a unique identifier for the touch press that persists until love.touchreleased. After that it is no longer unique.
x and y are the coordinates of the touch event in pixels within the window.
dx and dy are the amount in pixels that the touch has moved since the last event.

Added love.touch.getTouchCount and love.touch.getTouch(index).

love.touch.getTouch takes an index (not the same as an id. indices are not stable and don't correspond to a unique touch press.)
It returns the id of the touch and its current x and y coordinates in pixels.

--HG--
branch : minor

src/modules/touch/wrap_Touch.cpp

@@ -0,0 +1,84 @@
+/**
+ * Copyright (c) 2006-2015 LOVE Development Team
+ *
+ * This software is provided 'as-is', without any express or implied
+ * warranty.  In no event will the authors be held liable for any damages
+ * arising from the use of this software.
+ *
+ * Permission is granted to anyone to use this software for any purpose,
+ * including commercial applications, and to alter it and redistribute it
+ * freely, subject to the following restrictions:
+ *
+ * 1. The origin of this software must not be misrepresented; you must not
+ *    claim that you wrote the original software. If you use this software
+ *    in a product, an acknowledgment in the product documentation would be
+ *    appreciated but is not required.
+ * 2. Altered source versions must be plainly marked as such, and must not be
+ *    misrepresented as being the original software.
+ * 3. This notice may not be removed or altered from any source distribution.
+ **/
+
+#include "common/config.h"
+
+// LOVE
+#include "wrap_Touch.h"
+
+#include "sdl/Touch.h"
+
+namespace love
+{
+namespace touch
+{
+
+#define instance() (Module::getInstance<Touch>(Module::M_TOUCH))
+
+int w_getTouchCount(lua_State *L)
+{
+	lua_pushinteger(L, instance()->getTouchCount());
+	return 1;
+}
+
+int w_getTouch(lua_State *L)
+{
+	int index = luaL_checkint(L, 1) - 1;
+
+	Touch::TouchInfo info;
+	luax_catchexcept(L, [&](){ info = instance()->getTouch(index); });
+
+	// Lets hope the ID can be accurately represented in a Lua number...
+	lua_pushnumber(L, (lua_Number) info.id);
+	lua_pushnumber(L, info.x);
+	lua_pushnumber(L, info.y);
+
+	return 3;
+}
+
+static const luaL_Reg functions[] =
+{
+	{ "getTouchCount", w_getTouchCount },
+	{ "getTouch", w_getTouch },
+	{ 0, 0 }
+};
+
+extern "C" int luaopen_love_touch(lua_State *L)
+{
+	Touch *instance = instance();
+	if (instance == nullptr)
+	{
+		luax_catchexcept(L, [&](){ instance = new love::touch::sdl::Touch(); });
+	}
+	else
+		instance->retain();
+
+	WrappedModule w;
+	w.module = instance;
+	w.name = "touch";
+	w.flags = MODULE_T;
+	w.functions = functions;
+	w.types = nullptr;
+
+	return luax_register_module(L, w);
+}
+
+} // touch
+} // love