Typo/style fixes in docs and code comments

Codespell(1)-pointed typos in files listed by `git ls-files`
(sans checkpatch.pl and possibly some others). Removed some
extra spaces. Added a few missing trailing periods.
`Default is ...`.  Added spaces in ' />' where missing
(sans e.g. wayland protocol and t/* files).
Fit some lines in docs/*.scd to 80 colums.

Used git grep commands (to find similar cases):
$ git grep -n '\S/>'
$ git grep -nF '.  '
$ git grep -n '[^\t*'\'',{#]\t'
$ git grep -ni 'default '

No functional change. No change in *.[ch] line numbers.

include/config/default-bindings.h

@@ -141,14 +141,14 @@ static struct key_combos {
  * <mouse>
  *   <context name="Maximize">
  *     <mousebind button="Left" action="Click">
- *       <action name="Focus"/>
- *       <action name="Raise"/>
- *       <action name="ToggleMaximize"/>
+ *       <action name="Focus" />
+ *       <action name="Raise" />
+ *       <action name="ToggleMaximize" />
  *     </mousebind>
  *   </context>
  *   <context name="Root">
  *     <mousebind direction="Up" action="Scroll">
- *       <action name="GoToDesktop" to="left" wrap="yes"/>
+ *       <action name="GoToDesktop" to="left" wrap="yes" />
  *     </mousebind>
  *   </context>
  * </mouse>