Pull request: improve installation script

Merge in DNS/adguard-home from 2542-2462-imp-script to master

Closes #2462.
Updates #2542.
Updates #2613.

Squashed commit of the following:

commit 4a74722
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Mon May 17 15:11:08 2021 +0300

    scripts: imp naming, docs

commit acbb586
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Mon May 17 15:05:57 2021 +0300

    scripts: imp fix

commit 6477701
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Mon May 17 14:54:05 2021 +0300

    scripts: fix bsd

commit 3308921
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Mon May 17 14:04:04 2021 +0300

    scripts: imp requirements checking

commit 453cf7a
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Mon May 17 13:54:38 2021 +0300

    scripts: fix docs

commit a222905
Merge: 0852c87 120ba96
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Mon May 17 13:50:45 2021 +0300

    Merge branch 'master' into 2542-2462-imp-script

commit 0852c87
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Mon May 17 13:49:27 2021 +0300

    scripts: add os-specific requirements check

commit 6313d8f
Merge: 1b4092d a031cae
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Fri May 14 19:46:57 2021 +0300

    Merge branch 'master' into 2542-2462-imp-script

commit 1b4092d
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Fri May 14 19:46:09 2021 +0300

    scripts: imp install.sh a little

commit 0584b30
Merge: 22621c8 9d788a2
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Fri May 14 19:27:47 2021 +0300

    Merge branch 'master' into 2542-2462-imp-script

commit 22621c8
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Fri May 14 19:25:47 2021 +0300

    all: imp code

commit a38f4ad
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Fri May 14 18:40:37 2021 +0300

    all: fix url variable

commit 238cb85
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Fri May 14 18:27:13 2021 +0300

    imp code quality

commit 0e36c12
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Fri May 14 16:34:49 2021 +0300

    all: fix typos

commit b20f0b7
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Thu Apr 29 14:02:40 2021 +0300

    all: imp installation script

CHANGELOG.md

@@ -19,16 +19,21 @@ and this project adheres to
 
 ### Added
 
+- Support for reinstall (`-r`) and uninstall (`-u`) flags in the installation
+  script ([#2462]).
 - Support for DHCP `DECLINE` and `RELEASE` message types ([#3053]).
 
 ### Fixed
 
+- Error when using installation script on some ARMv7 devices ([#2542]).
 - DHCP leases validation ([#3107], [#3127]).
 - Local PTR request recursion in Docker containers ([#3064]).
 - Ignoring client-specific filtering settings when filtering is disabled in
   general settings ([#2875]).
 - Disallowed domains are now case-insensitive ([#3115]).
 
+[#2462]: https://github.com/AdguardTeam/AdGuardHome/issues/2462
+[#2542]: https://github.com/AdguardTeam/AdGuardHome/issues/2542
 [#2875]: https://github.com/AdguardTeam/AdGuardHome/issues/2875
 [#3053]: https://github.com/AdguardTeam/AdGuardHome/issues/3053
 [#3064]: https://github.com/AdguardTeam/AdGuardHome/issues/3064

HACKING.md

@@ -313,6 +313,8 @@ on GitHub and most other Markdown renderers. -->
 
  *  Avoid bashisms and GNUisms, prefer POSIX features only.
 
+ *  Avoid spaces between patterns of the same `case` condition.
+
  *  Prefer `'raw strings'` to `"double quoted strings"` whenever possible.
 
  *  Put spaces within `$( cmd )`, `$(( expr ))`, and `{ cmd; }`.
@@ -328,10 +330,10 @@ on GitHub and most other Markdown renderers. -->
  *  UPPERCASE names for external exported variables, lowercase for local,
     unexported ones.
 
- *  Use `set -e -f -u` and also `set -x` in verbose mode.
-
  *  Use `readonly` liberally.
 
+ *  Use `set -e -f -u` and also `set -x` in verbose mode.
+
  *  Use the `"$var"` form instead of the `$var` form, unless word splitting is
     required.
 
@@ -356,6 +358,7 @@ on GitHub and most other Markdown renderers. -->
  *  When using `test` (aka `[`), spell compound conditions with `&&`, `||`, and
     `!` **outside** of `test` instead of `-a`, `-o`, and `!` inside of `test`
     correspondingly.  The latter ones are pretty much deprecated in POSIX.
+    Also, prefer `!= ''` form instead of `-n` to check if string is empty.
 
     See also: “[Problems With the `test` Builtin: What Does `-a` Mean?]”.
 

README.md

@@ -68,9 +68,17 @@ It operates as a DNS server that re-routes tracking domains to a "black hole", t
 ### Automated install (Linux and Mac)
 Run the following command in your terminal:
 ```
-curl -sSL https://raw.githubusercontent.com/AdguardTeam/AdGuardHome/master/scripts/install.sh | sh
+curl -s -S -L https://raw.githubusercontent.com/AdguardTeam/AdGuardHome/master/scripts/install.sh | sh -s -- -v
 ```
 
+The script also accepts some options:
+* `-c <channel>` to use specified channel.
+* `-r` to reinstall AdGuard Home;
+* `-u` to uninstall AdGuard Home;
+* `-v` for verbose output;
+
+Note that options `-r` and `-u` are mutually exclusive.
+
 ### Alternative methods
 
 #### Manual installation