Don't use features which are not yet present in the version of ucode
currently shipped with OpenWrt (such as `fs.access()` or assuming raw
mode by default).
Fix syntax error in main executable.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>
(cherry picked from commit 74caff0d59)

* Fix build which was broken by a wrong path in the Makefile.

Adapt to ucode commit 4618807 ("main: rework CLI frontend"):
 * ucode now no longer needs the {% %} around each code file, remove
   that and safe one level of indentation.
 * ARGV now no longer includes ucode executable and script itself

Fixes: 6350c7bc6 ("uvol: replace with re-write in ucode")
Signed-off-by: Daniel Golle <daniel@makrotopia.org>
(cherry picked from commit 22d202e3a56d6756543713ec2a2af3c65da31572)

Replace previous Shell draft-quality implementation of uvol with a
rewrite in ucode[1].
While the new code is slightly larger, it performs much better (as
we no longer fork() for parsing strings like in Shell with grep, sed
and friends).

Before:
  time uvol list -j
  [ ... ]
  real	0m 0.82s
  user	0m 0.13s
  sys	0m 0.10s

After:
  time uvol list -j
  [ ... ]
  real	0m 0.47s
  user	0m 0.05s
  sys	0m 0.05s

[1]: https://github.com/jow-/ucode
Signed-off-by: Daniel Golle <daniel@makrotopia.org>
(cherry picked from commit 6350c7bc63)