feat: add base classes for handling completion

src/commands/completion_autodetect.cr

@@ -0,0 +1,17 @@
+require "./abstract_command"
+
+module GX::Commands
+  class CompletionAutodetect < AbstractCommand
+    def initialize(@config : GX::Config)
+    end
+
+    def execute
+      STDERR.puts "FIXME: Completion auto-detection isn't implemented yet. Please select one of the following: --bash or --zsh"
+      exit(0)
+    end
+
+    def self.handles_mode
+      GX::Types::Mode::CompletionAutodetect
+    end
+  end
+end

src/commands/completion_bash.cr

@@ -0,0 +1,17 @@
+require "./abstract_command"
+
+module GX::Commands
+  class CompletionBash < AbstractCommand
+    def initialize(@config : GX::Config)
+    end
+
+    def execute
+      completion_bash = FileStorage.get("completion.bash")
+      STDOUT.puts completion_bash.gets_to_end
+    end
+
+    def self.handles_mode
+      GX::Types::Mode::CompletionBash
+    end
+  end
+end

src/commands/completion_zsh.cr

@@ -0,0 +1,17 @@
+require "./abstract_command"
+
+module GX::Commands
+  class CompletionZsh < AbstractCommand
+    def initialize(@config : GX::Config)
+    end
+
+    def execute
+      completion_bash = FileStorage.get("completion.zsh")
+      STDOUT.puts completion_bash.gets_to_end
+    end
+
+    def self.handles_mode
+      GX::Types::Mode::CompletionZsh
+    end
+  end
+end