Pull txt/ and doc/ updates from Gene Cumm,
* 'doc-for-mfleming' of git://github.com/geneC/syslinux:
txt/syslinux.txt: rewrap long command
txt/Makefile: add isolinux.txt, pxelinux.txt
txt/: Add isolinux.txt, pxelinux.txt
txt/syslinux-cli.txt: Version on Ctrl-N
txt/Makefile: order-only prerequisite
txt/: Add common file for derivatives
txt/syslinux.cfg.txt: Updates
txt/syslinux.txt: synopsis, extlinux.sys, wrap long command
txt/syslinux-cli.txt: Path rules
txt/syslinux.cfg.txt: Add SENDCOOKIES, example config
txt/syslinux.cfg.txt: Add SYSAPPEND
doc/syslinux.txt: grammar
Fix SERIAL directive in docs