add a simple pager
add a simple pager

The u-root less program has a lot of issues that make it
'less' useful, especially in firmware environments:

1) can't read from a pipe
2) can't read from any file that can't be mmap'ed
3) can't be in a pipeline
4) needs builtin terminfo support and environment variables
5) at least for me, has a weird error that won't let it read commands at all,
   so I'm always stuck seeing just one page of text

page is a dead simple pager modeled on the one from Plan 9.
It's already more useful to me than our less program.

And it's got far less footprint: 2.22M vs. 3.38M

Signed-off-by: Ronald G. Minnich <f569d0af9a3481c4007b95c7180d6c41009f2513@gmail.com>

u-root/u-root,GanShun/u-root,GanShun/u-root,GanShun/u-root,hugelgupf/u-root,hugelgupf/u-root,u-root/u-root,u-root/u-root,hugelgupf/u-root,hugelgupf/u-root