OPOSD enhancements
- extended horizontal and vertical resolution to full screen for PAL:
  400x288 and NTSC: 368x241
- changed hsync trigger to rising edge to get 4 more desperately needed
  microseconds for the extended resolution
- switched to direct bit manipulations in interrrupt context to be
  fast, desperately needed for the extended resolution
- line and column offsets are now realized in low level functions
- refactored RAM consuming GRAPHICS_HDEADBAND/GRAPHICS_VDEADBAND
  stuff to reasonable alignment in low level functions
- refactored APPLY_HDEADBAND and APPLY_VDEADBAND stuff to
  reasonable alignment in low level functions
- refactored the '- 8' and 'clear the last 8 columns at every
  draw' stuff to reasonable buffer trailing 0 byte for SPI out bits

- some minor refactorings
- proof for PAL  video-link:  http://youtu.be/aj0-YBIAyL0
- proof for NTSC video-link:  http://youtu.be/UFSdXIXbFaY