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/scaled-buffer/scaled-buffer.h

@@ -130,7 +130,7 @@ void scaled_buffer_request_update(struct scaled_buffer *self,
 
 /**
  * scaled_buffer_invalidate_sharing - clear the list of entire cached
- * scaled_buffers used to share visually dupliated buffers. This should
+ * scaled_buffers used to share visually duplicated buffers. This should
  * be called on Reconfigure to force updates of newly created
  * scaled_buffers rather than reusing ones created before Reconfigure.
  */