Added prerun command annotation & implementation

src/cligen/annotations.cr

@@ -14,6 +14,9 @@ module CliGen
   annotation Selection
   end
  
+  annotation PreRunCommand
+  end
+
   annotation SubCommand
   end
 end

src/cligen/command_node.cr

@@ -244,6 +244,10 @@ module CliGen
       {% unless T == Nil %}
       unless passed_execution
         cls = T.new(handler: self.as(CliGen::BaseCommandNode))
+        {% prerun = T.methods.select(&.annotation(CliGen::PreRunCommand)) %}
+        {% for cmd in prerun %}
+        cls.{{cmd.name}}
+        {% end %}
         {% subcmds = T.methods.select(&.annotation(CliGen::SubCommand)) %}
         {% begin %}
         case matched_subcommand