Refactor the long if-statement in Validator.

      # Checks for fatal problems in command line options.

      # Exits with error message when such problem found.

      def validate!

        if @opts.input_files.length == 0 && !@opts.welcome && !@opts.guides && !@opts.videos && !@opts.examples

          Logger.fatal("You should specify some input files, otherwise there's nothing I can do :(")

          exit(1)

        elsif @opts.output_dir == :stdout && !@opts.export

          Logger.fatal("Output to STDOUT only works when using --export option")

          exit(1)

        elsif ![nil, :full, :api, :examples].include?(@opts.export)

          Logger.fatal("Unknown export format: #{@export}")

          exit(1)

        elsif @opts.output_dir != :stdout

          if !@opts.output_dir

            Logger.fatal("You should also specify an output directory, where I could write all this amazing documentation")

            exit(1)

        input_files_present

        output_dir_present

        valid_export_format

        template_files_present

      end

      private

      def input_files_present

        if @opts.input_files.empty? && !@opts.welcome && !@opts.guides && !@opts.videos && !@opts.examples

          fatal("Please specify some input files, otherwise there's nothing I can do :(")

        end

      end

      def output_dir_present

        if @opts.output_dir == :stdout

          # No output dir needed for export

          if !@opts.export

            fatal("Output to STDOUT only works when using --export option")

          end

        elsif !@opts.output_dir

          fatal("Please specify an output directory, where to write all this amazing documentation")

        elsif File.exists?(@opts.output_dir) && !File.directory?(@opts.output_dir)

            Logger.fatal("The output directory is not really a directory at all :(")

            exit(1)

          fatal("The output directory is not really a directory at all :(")

        elsif !File.exists?(File.dirname(@opts.output_dir))

            Logger.fatal("The parent directory for #{@opts.output_dir} doesn't exist")

            exit(1)

          elsif !@opts.export && !File.exists?(@opts.template_dir + "/extjs")

            Logger.fatal("Oh noes!  The template directory does not contain extjs/ directory :(")

            Logger.fatal("Please copy ExtJS over to template/extjs or create symlink.")

            Logger.fatal("For example:")

            Logger.fatal("    $ cp -r /path/to/ext-4.0.0 " + @opts.template_dir + "/extjs")

            exit(1)

          elsif !@opts.export && !File.exists?(@opts.template_dir + "/resources/css")

            Logger.fatal("Oh noes!  CSS files for custom ExtJS theme missing :(")

            Logger.fatal("Please compile SASS files in template/resources/sass with compass.")

            Logger.fatal("For example:")

            Logger.fatal("    $ compass compile " + @opts.template_dir + "/resources/sass")

            exit(1)

          fatal("The parent directory for #{@opts.output_dir} doesn't exist")

        end

      end

      def valid_export_format

        if ![nil, :full, :api, :examples].include?(@opts.export)

          fatal("Unknown export format: #{@export}")

        end

      end

      def template_files_present

        if @opts.export

          # Don't check these things when exporting

        elsif !File.exists?(@opts.template_dir + "/extjs")

          fatal("Oh noes!  The template directory does not contain extjs/ directory :(")

          fatal("Please copy ExtJS over to template/extjs or create symlink.")

          fatal("For example:")

          fatal("    $ cp -r /path/to/ext-4.0.0 " + @opts.template_dir + "/extjs")

        elsif !File.exists?(@opts.template_dir + "/resources/css")

          fatal("Oh noes!  CSS files for custom ExtJS theme missing :(")

          fatal("Please compile SASS files in template/resources/sass with compass.")

          fatal("For example:")

          fatal("    $ compass compile " + @opts.template_dir + "/resources/sass")

        end

      end

      def fatal(smg)

        Logger.fatal(msg)

        exit(1)

      end

    end