LOW-RES FRAMEBUFFER RENDERING

```
Description: There are obvious issues in the low-res, < 8 BPP, implementation of
the framebuffer rendering logic of graphics/nxglib/fb. I see two
obvious problems in reviewing nxglib_copyrectangle():

1. The masking logic might work 1 BPP, but is insufficient for other
resolutions like 2-BPP and 4-BPP.
2. The use of lnlen will not handle multiple bits per pixel. It
would need to be converted to a byte count.

The function PDC_copy_glyph() in the file apps/graphics/pdcurs34/nuttx/pdcdisp.c
derives from nxglib_copyrectangle() and all of those issues have been
resolved in that file.

Other framebuffer rendering functions probably have similar issues.
Status: Open
Priority: Low. It is not surprising that there would be bugs in this logic:
I have never encountered a hardware framebuffer with sub-byte pixel
depth. If such a beast ever shows up, then this priority would be
higher.
```