Implement blargg ntsc filters

- this implements blargg's nes ntsc filters using core options
- an optional height doubling is also added but disabled for performance reasons (might make that optional as a core option)
- since PS2 and PSP have their own blitter branches, these platforms do not have the ntsc filters since i dont have the means to test on those systems.
- compile with HAVE_NTSC=1 to have these options, HAVE_NTSC=0 disabled filter including core options
- HAVE_NTSC=1 is set as default, other than PS2 and PSP as stated above.

src/ntsc/readme.txt

@@ -0,0 +1,61 @@
+nes_ntsc 0.2.2: NES NTSC Video Filter
+-------------------------------------
+This library filters a NES image to match what a TV would show, allowing
+an authentic image in an emulator. It uses a highly optimized algorithm
+to perform the same signal processing as an NTSC decoder in a TV, giving
+very similar pixel artifacts and color bleeding. The usual picture
+controls can be adjusted: hue, saturation, contrast, brightness, and
+sharpness. Additionally, the amount of NTSC chroma and luma artifacts
+can be reduced, allowing an image that corresponds to composite video
+(artifacts), S-video (color bleeding only), RGB (clean pixels), or
+anywhere inbetween.
+
+The output is scaled to the proper horizontal width, leaving it up the
+emulator to simply double the height. An optional even/odd field merging
+feature is provided to reduce flicker when the host display's refresh
+rate isn't 60 Hz. Specialized blitters can be easily written using a
+special interface, allowing customization of input and output pixel
+formats, optimization for the host platform, and efficient scanline
+doubling.
+
+Blitting a 256x240 source image to a 602x240 pixel 16-bit RGB memory
+buffer at 60 frames per second uses 8% CPU on a 2.0 GHz Athlon 3500+ and
+40% CPU on a 10-year-old 400 MHz G3 PowerMac.
+
+Author  : Shay Green <gblargg@gmail.com>
+Website : http://www.slack.net/~ant/
+Forum   : http://groups.google.com/group/blargg-sound-libs
+License : GNU Lesser General Public License (LGPL)
+Language: C or C++
+
+
+Getting Started
+---------------
+Build a program from demo.c, nes_ntsc.c, and the SDL multimedia library
+(see http://libsdl.org/). Run it with "test.bmp" in the same directory
+and it should show the filtered image. See demo.c for more.
+
+See nes_ntsc.txt for documentation and nes_ntsc.h for reference. Post to
+the discussion forum for assistance.
+
+
+Files
+-----
+readme.txt          Essential information
+nes_ntsc.txt        Library documentation
+changes.txt         Changes made since previous releases
+license.txt         GNU Lesser General Public License
+
+benchmark.c         Measures frame rate and processor usage of library
+demo.c              Displays and saves NTSC filtered image
+demo_impl.h         Internal routines used by demo
+test.bmp            Test image for demo
+tests/              Test ROMs to verify burst phase operation
+
+nes_ntsc_config.h   Library configuration (modify as needed)
+nes_ntsc.h          Library header and source
+nes_ntsc.c
+nes_ntsc_impl.h
+
+-- 
+Shay Green <gblargg@gmail.com>