Implement ruby feature loading (-r CLI option)

features/cli/ruby_features.feature

@@ -0,0 +1,5 @@
+Feature: ruby feature require CLI option
+
+  Scenario: requires a ruby feature
+    When I run uhwm with option -v -r abbrev
+    Then the current output must match /load.+abbrev.+ruby feature/i

features/steps/output_steps.rb

@@ -23,6 +23,7 @@ options:
     -h, --help                       print this message
     -v, --version                    enable verbose mode
     -d, --debug                      enable debug mode
+    -r, --require PATH               require ruby feature
   eoh
 end