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/img/img-xbm.c

@@ -226,7 +226,7 @@ out:
 
 /*
  * Openbox built-in icons are not bigger than 8x8, so have only written this
- * function to cope wit that max size
+ * function to cope with that max size
  */
 #define LABWC_BUILTIN_ICON_MAX_SIZE (8)