[ruby/irb] Add workspace category

(https://github.com/ruby/irb/pull/661)

* Create a new Workspace command category

* Update readme

https://github.com/ruby/irb/commit/310650c213

lib/irb/cmd/chws.rb

@@ -13,7 +13,7 @@ module IRB
   module ExtendCommand
 
     class CurrentWorkingWorkspace < Nop
-      category "IRB"
+      category "Workspace"
       description "Show the current workspace."
 
       def execute(*obj)
@@ -22,7 +22,7 @@ module IRB
     end
 
     class ChangeWorkspace < Nop
-      category "IRB"
+      category "Workspace"
       description "Change the current workspace to an object."
 
       def execute(*obj)

lib/irb/cmd/pushws.rb

@@ -12,7 +12,7 @@ module IRB
 
   module ExtendCommand
     class Workspaces < Nop
-      category "IRB"
+      category "Workspace"
       description "Show workspaces."
 
       def execute(*obj)
@@ -21,7 +21,7 @@ module IRB
     end
 
     class PushWorkspace < Workspaces
-      category "IRB"
+      category "Workspace"
       description "Push an object to the workspace stack."
 
       def execute(*obj)
@@ -31,7 +31,7 @@ module IRB
     end
 
     class PopWorkspace < Workspaces
-      category "IRB"
+      category "Workspace"
       description "Pop a workspace from the workspace stack."
 
       def execute(*obj)