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.

docs/labwc.1.scd

@@ -66,7 +66,7 @@ the `--exit` and `--reconfigure` options use.
 	Manager, or the Window Manager can be launched independently first. On
 	Wayland, the Compositor is both Display Server and Window Manager, so
 	the described session management mechanisms do not work because the
-	Compositor needs to be running before the session can function.  As some
+	Compositor needs to be running before the session can function. As some
 	session clients support both X11 and Wayland, this command line option
 	avoids re-writes and fragmentation.
 
@@ -75,7 +75,7 @@ the `--exit` and `--reconfigure` options use.
 	(i.e. nested in a compositor). <fmtstr> is a format string to be used as
 	the window title, replacing `%o` with the name of the output
 	region. This is useful when simulating multiple screens, such as with
-	running labwc with the enviornment variable `WLR_WL_OUTPUTS=2`. In this
+	running labwc with the environment variable `WLR_WL_OUTPUTS=2`. In this
 	case, `%o` will be unique per simulated screen.
 
 *-v, --version*