- Add XTCH container format support (.xtch extension)
- Add XTH page format with two bit-plane, column-major storage
- Update XtcParser to handle both XTC/XTCH magic and XTG/XTH pages
- Update XtcReaderActivity for XTH column-major rendering
- Update cover BMP generation for 2-bit grayscale
- Add README with format documentation
XTH format details:
- Two bit planes stored sequentially (Bit1, then Bit2)
- Column-major order, scanned right to left
- 8 vertical pixels per byte (MSB = topmost)
- Grayscale: 0=White, 1=Dark Grey, 2=Light Grey, 3=Black
