kconfig: fix trivial typos and update mconf documentation

This fixes lots of typos in comments and strings.

It also updates the documentation strings in mconf to reflect the changes in
the user interface from the two commits

6364fd0c
  menuconfig: Add Save/Load buttons
1bdbac47
  menuconfig: Get rid of the top-level entries for "Load an Alternate/Save an Alternate"

And it updates the layout of the example search result, i. e. moves down the
"Defined at" and "Depends on" lines and adds a symbol state ([=n]) to the
symbol in the "Selected by" line.

Furthermore, the help texts now should fit in 80 columns again when viewed
in mconf.

Signed-off-by: Martin Walch <walch.martin@web.de>
Reviewed-by: Jean Delvare <jdelvare@suse.de>
Reviewed-by: Wang YanQing <udknight@gmail.com>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>