Output: add supportsItalics and supportsStrikethrough to check for feature support

src/Graphics/Vty/Output/Interface.hs

@@ -101,6 +101,10 @@ data Output = Output
     , ringTerminalBell :: IO ()
       -- | Returns whether the terminal has an audio bell feature.
     , supportsBell :: IO Bool
+      -- | Returns whether the terminal supports italicized text.
+    , supportsItalics :: IO Bool
+      -- | Returns whether the terminal supports strikethrough text.
+    , supportsStrikethrough :: IO Bool
     }
 
 displayContext :: Output -> DisplayRegion -> IO DisplayContext

src/Graphics/Vty/Output/Mock.hs

@@ -48,6 +48,8 @@ mockTerminal r = liftIO $ do
             , releaseDisplay = return ()
             , ringTerminalBell = return ()
             , supportsBell = return False
+            , supportsItalics = return False
+            , supportsStrikethrough = return False
             , setDisplayBounds = const $ return ()
             , displayBounds = return r
             , outputByteBuffer = \bytes -> do

src/Graphics/Vty/Output/TerminfoBased.hs

@@ -168,6 +168,10 @@ reserveTerminal termName outFd = do
                 sendCap setDefaultAttr []
                 maybeSendCap cnorm []
             , supportsBell = return $ isJust $ ringBellAudio terminfoCaps
+            , supportsItalics = return $ (isJust $ enterItalic (displayAttrCaps terminfoCaps)) &&
+                                         (isJust $ exitItalic (displayAttrCaps terminfoCaps))
+            , supportsStrikethrough = return $ (isJust $ enterStrikethrough (displayAttrCaps terminfoCaps)) &&
+                                               (isJust $ exitStrikethrough (displayAttrCaps terminfoCaps))
             , ringTerminalBell = maybeSendCap ringBellAudio []
             , reserveDisplay = do
                 -- If there is no support for smcup: Clear the screen