docproc: style & typo cleanups

- fix typos/spellos in docproc.c and Makefile
- add a little whitespace {while, switch} (coding style)
- use NULL instead of 0 for pointer testing

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>