txt/: Add new AsciiDoc formatted documentation

Signed-off-by: Gene Cumm <gene.cumm@gmail.com>
Makefile: add txt/

Signed-off-by: Gene Cumm <gene.cumm@gmail.com>
NEWS: add txt/

Signed-off-by: Gene Cumm <gene.cumm@gmail.com>
txt/: Remove COMBOOT as of 5.00; spelling; add PATH

Also changing markup for AsciiDoc

Signed-off-by: Gene Cumm <gene.cumm@gmail.com>
txt/Makefile: make directories