Multitouch support for SDL2

Add SDL Features.hpp to define HAVE_MULTI_TOUCH if SDL2 is enabled and
handle SDL_FINGERDOWN / SDL_FINGERUP events to call OnMultiTouchDown() /
OnMultiTouchUp(). This change does not affect SDL_MOUSEBUTTONDOWN /
SDL_MOUSEBUTTONUP event handling, these two events are still triggered
for touch events as well.
Battery state information with SDL2

Add an implementation for UpdateBatteryInfo() using SDL_GetPowerInfo(),
if SDL2 is enabled.
Ensure that SDL textures are created in the correct pixel format

Create textures with SDL_PIXELFORMAT_RGB888 instead of
SDL_PIXELFORMAT_UNKNOWN. Furthermore, when the texture is recrated in
OnResize(), use the same texture pixel format which the previous texture
instance had.
OpenGL ES 2.0 support when using SDL2

When HAVE_GLES2 is defined, and SDL2 is used, include SDL_opengles2.h
instead of SDL_opengles.h. And set SDL GL attributes
SDL_GL_CONTEXT_MAJOR_VERSION and SDL_GL_CONTEXT_MINOR_VERSION, so that
SDL creates an OpenGL ES 2.0 context
Compile warning fix for clang

clang complained about incorrect brackets being used for uint8x8x2_t
variable initailizations.
Replacement for "ld -b binary" resource embedding mechanism

"ld -b binary" is not supported by all linkers, particularly not by the
Apple ld64 linker. Now, a small (and portable) assembler program is
generated compiled by the EmbedFileInObjectFile.pm perl module to
generate .o files which are compatible with those compiled with "ld -b
binary". The .mk include order is changed so that the AS variable
(defined in compile.mk) is correctly initialized for resource.mk and
libdata.mk.
Asset: Add IsApple(), IsMacOSX() and IsIOS()
Add HOST_IS_X86_32 and HOST_IS_X86_64 variables
Use -isystem instead of -I for freetype include directory
Use -isystem instead of -I for libpng include directory
Revise build system for darwin targets

This adds support for the toolchain / library set which can be built
using the scripts from
https://github.com/felixhaedicke/DarwinToolchainBuilder
This also enabled cross compiling support for Darwin targets.
The hardcoded library paths to /opt/local/lib are no longer needed and
removed.
Add IOS build target

Add support for building for iPhone and iPad devices. For this target,
SDL2 and OpenGL ES 2.0 is used.
Correct font paths for Apple targets

Add font paths for iOS devices and correct the paths for Mac OS X
Add support for compiling Objective C++ files
Add support for internal GPS sensors for Apple devices using CoreLocation

Add support for an "internal sensors" device for Mac OS X and iOS. This
implementation uses the CoreLocation framework.
Show correct version information on iOS and Mac OS X devices
Set the screen DPI value to 300 for iOS devices
Adjust default font size for iOS devices
OpenGL/Init: Compile fix for iOS

There are no preprocessor definitions GL_STENCIL_INDEX1_OES and
GL_STENCIL_INDEX4_OES in the iOS SDK
Keep screen on when using SDL2

Set hint SDL_HINT_IDLE_TIMER_DISABLED for SDL2 to keep the screen on.