Proofreading, typo and grammar fixes to Ch 10 User's Guide.

Various cleanups to Chapter 10 of the User's Guide, no functional
changes.

Change-Id: I055d032eacc8e85b1d8edbd4bcc505f6f0feaa49
Signed-off-by: Robert P. J. Day <rpjday@crashcourse.ca>
Reviewed-on: http://openocd.zylin.com/1861


Tested-by: jenkins
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>