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.

src/config/rcxml.c

@@ -613,9 +613,9 @@ fill_mousebind(xmlNode *node, const char *context)
 	/*
 	 * Example of what we are parsing:
 	 * <mousebind button="Left" action="DoubleClick">
-	 *   <action name="Focus"/>
-	 *   <action name="Raise"/>
-	 *   <action name="ToggleMaximize"/>
+	 *   <action name="Focus" />
+	 *   <action name="Raise" />
+	 *   <action name="ToggleMaximize" />
 	 * </mousebind>
 	 */