Adds support for running as a forking process in the foreground

Reason: The `script/delayed_job` process (described above) uses the
[Daemons](https://github.com/thuehlinger/daemons) gem which has several
undesirable behaviors when running inside a container (Docker, etc.):
- The parent process spawns a background child process then exits immediately,
which causes the container to shutdown.
- The worker processes are detached from the parent, which prevents logging to `STDOUT`.

The `--fork` option solves this by running workers in a foreground process tree.
When using `--fork` the `daemons` gem is not required.

The command script requires changing the following line to enable this:

# always daemonizes, never forks
Delayed::Command.new(ARGV).daemonize

must now be:

# daemonize by default unless --fork specified
Delayed::Command.new(ARGV).launch

In addition, there are several quality of life improvements added to the Command script:
- Command: Add --pools arg as an alias for --pool, and allow pipe-delimited pool definitions
- Command: Add --num-worker arg as an alias for -n / --number-of-workers (and deprecate --number-of-workers)
- Command: Pool parsing code has been extracted to PoolParser class
- Command: Add -v / --verbose switch which sets quiet=false on workers
- Command: Add -x switch as alias for --exit-on-complete
- Command: Add STDERR warning num-workers less than 1
- Command: Add STDERR warning if num-workers and pools both specified (pools overrides num-workers as per existing behavior)
- Command: Add STDERR warning if queues and pools both specified (pools overrides num-workers as per existing behavior)

The Rake script has also been enhanced:
- Rake: Uses Forking launcher under the hood
- Rake: Add support for NUM_WORKERS and POOLS args

.github/workflows/ci.yml

@@ -9,32 +9,51 @@ on:
 jobs:
   test:
     runs-on: ubuntu-latest
+    continue-on-error: ${{ matrix.experimental }}
     strategy:
       fail-fast: false
       matrix:
-        ruby: [2.5, 2.6, 2.7, jruby, jruby-head, ruby-head]
+        ruby:
+          - '2.5'
+          - '2.6'
+          - '2.7'
+          - '3.0'
+          - 'jruby'
         rails_version:
-          - '5.2.0'
-          - '6.0.0'
-          - '6.1.0.rc2'
-          - 'edge'
+          - '6.0'
+          - '6.1'
         include:
-          #
-          # The past
-          #
-          # EOL Active Record
-          - ruby: 2.2
-            rails_version: '3.2.0'
-          - ruby: 2.1
-            rails_version: '4.1.0'
-          - ruby: 2.4
-            rails_version: '4.2.0'
-          - ruby: 2.4
-            rails_version: '5.0.0'
-          - ruby: 2.5
-            rails_version: '5.1.0'
-
-    continue-on-error: ${{ matrix.rails_version == 'edge' || endsWith(matrix.ruby, 'head') }}
+          # Older Rails
+          - ruby: '2.2'
+            rails_version: '3.2'
+          - ruby: '2.1'
+            rails_version: '4.1'
+          - ruby: '2.4'
+            rails_version: '4.2'
+          - ruby: '2.4'
+            rails_version: '5.0'
+          - ruby: '2.5'
+            rails_version: '5.1'
+          - ruby: '2.5'
+            rails_version: '5.2'
+          - ruby: 'jruby'
+            rails_version: '5.2'
+          # Experimental
+          - ruby: 'ruby-head'
+            rails_version: '6.1'
+            experimental: true
+          - ruby: 'jruby-head'
+            rails_version: '6.1'
+            experimental: true
+          - ruby: '2.7'
+            rails_version: 'edge'
+            experimental: true
+          - ruby: '3.0'
+            rails_version: 'edge'
+            experimental: true
+          - ruby: 'jruby'
+            rails_version: 'edge'
+            experimental: true
 
     steps:
     - uses: actions/checkout@v2

.rubocop.yml

@@ -127,6 +127,9 @@ SignalException:
 SpaceInsideHashLiteralBraces:
   EnforcedStyle: no_space
 
+Style/SpecialGlobalVars:
+  Enabled: false
+
 Style/SymbolArray:
   Enabled: false