Add clipboard helper functions and bind them

\cy copies, \cv pastes.

share/functions/fish_clipboard_copy.fish

@@ -0,0 +1,7 @@
+function fish_clipboard_copy
+	if type -q pbcopy
+        commandline | pbcopy
+    else if type -q xsel
+        commandline | xsel --clipboard
+    end
+end

share/functions/fish_clipboard_paste.fish

@@ -0,0 +1,7 @@
+function fish_clipboard_paste
+	if type -q pbpaste
+        commandline -i (pbpaste)
+    else if type -q xsel
+        commandline -i (xsel --clipboard)
+    end
+end

share/functions/fish_default_key_bindings.fish

@@ -18,7 +18,8 @@ function fish_default_key_bindings -d "Default (Emacs-like) key bindings for fis
 	bind $argv \r execute
 
 	bind $argv \ck kill-line
-	bind $argv \cy yank
+    bind $argv \cy fish_clipboard_copy
+    bind $argv \cv fish_clipboard_paste
 	bind $argv \t complete
 
 	bind $argv \e\n "commandline -i \n"