Add --bdctl-url option

[ObserverOfTime]

This option allows users to specify the URL used when upgrading betterdiscordctl.
It can be used to apply temporary or pre-release fixes. Example:

betterdiscordctl upgrade --bdctl-url \
  'https://raw.githubusercontent.com/bb010g/betterdiscordctl/temp-fix/betterdiscordctl'

I've also updated the path of the flatpak version (see #45 (comment))
and removed the redirection to FD 3 because it fails with sh: 3: Bad file descriptor.

Moreover, it doesn't seem like snap actually uses XDG_CONFIG_HOME so I've removed that.

@bb010g I believe these changes require a review.

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This change is 

[bb010g]

Reviewed 2 of 2 files at r1.
Reviewable status: all files reviewed, 5 unresolved discussions (waiting on @ObserverOfTime)

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betterdiscordctl, line 24 at r1 (raw file):

snap=
flatpak=
bdctl_url='https://git.io/bdctl'

I would really prefer if we didn't use this. URL shorteners aren't clear, and we're not hurting on bytes.

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betterdiscordctl, line 60 at r1 (raw file):

      --bdctl-url=URL            Use the specified URL for upgrading BDCTL
                                 (default 'https://git.io/bdctl')

This can just be --upgrade-url=URL, "URL to upgrade this program with". Variables should be appropriately renamed.

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betterdiscordctl, line 348 at r1 (raw file):

  if [[ $semver_diff -eq 1 ]]; then
    printf 'Downloading betterdiscordctl...\n' >&2
    if curl -LSso "$SOURCE" "$bdctl_url"; then

Keeping the -L is good, even without the shortener.

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betterdiscordctl, line 400 at r1 (raw file):

          if [[ -z $modules ]]; then
            bdc_find_modules
          else # --modules

Please don't use trailing comments.

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betterdiscordctl, line 428 at r1 (raw file):

    # shellcheck disable=SC2016
    # Expansion should happen inside snap's shell.
    xdg_config=$("$snap_bin" run --shell discord <<< 'echo $SNAP_USER_DATA/.config 1>&3' 3>&1)

The quotes should definitely be kept ($SNAP_USER_DATA could contain multiple spaces). This should probably be $'printf \'%s\\n\' "$SNAP_USER_DATA/.config" 1>&3' to avoid an echo that tries to parse a strange $SNAP_USER_DATA starting with - as an option.

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README.md, line 102 at r1 (raw file):

  option argument will be used as the flatpak command to call.

* `--bdctl-url` (default `https://git.io/bdctl`)

Also update for --update-url.

[ObserverOfTime]

Reviewable status: all files reviewed, 5 unresolved discussions (waiting on @bb010g and @ObserverOfTime)

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betterdiscordctl, line 24 at r1 (raw file):

Previously, bb010g (bb010g) wrote…

I would really prefer if we didn't use this. URL shorteners aren't clear, and we're not hurting on bytes.

I shortened it to avoid going over 80 characters in the CLI help text.

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betterdiscordctl, line 400 at r1 (raw file):

Previously, bb010g (bb010g) wrote…

Please don't use trailing comments.

What's wrong with trailing comments?

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betterdiscordctl, line 428 at r1 (raw file):

Previously, bb010g (bb010g) wrote…

The quotes should definitely be kept ($SNAP_USER_DATA could contain multiple spaces). This should probably be $'printf \'%s\\n\' "$SNAP_USER_DATA/.config" 1>&3' to avoid an echo that tries to parse a strange $SNAP_USER_DATA starting with - as an option.

echo handles multiple spaces just fine but you're right about -.

Shouldn't the command be $'printf -- \'%s/.config\\n\' "$SNAP_USER_DATA" 1>&3' though? And the same should be done for the other echos.