Add version CLI option

features/cli/version.feature

@@ -0,0 +1,6 @@
+Feature: version CLI option
+
+  Scenario: prints the current version on standard output
+    When I run uhwm with option --version
+    Then uhwm must terminate successfully
+    And the output must contain exactly the version

features/steps/output_steps.rb

@@ -10,9 +10,15 @@ options:
     -r, --require PATH               require ruby feature
     -l, --layout LAYOUT              specify layout
     -w, --worker WORKER              specify worker
+    -V, --version                    print version
   eoh
 end
 
+Then /^the output must contain exactly the version$/ do
+  #require File.expand_path('../lib/uh/wm/version', __FILE__)
+  assert_exact_output "%s\n" % Uh::WM::VERSION, all_output
+end
+
 Then /^the output must match \/([^\/]+)\/([a-z]*)$/ do |pattern, options|
   uhwm_wait_output Regexp.new(pattern, options)
 end