Add "o" alias for "open" or "xdg-open"

xonsh/alias.xsh

@@ -10,3 +10,8 @@ aliases["pubip"] = "curl icanhazip.com"
 
 aliases["ll"] = lambda args: $[$LC_COLLATE='C' ls -lAh --color @(args)]
 aliases["ls"] = "ls --color"
+
+if ON_DARWIN:
+    aliases["o"] = "open"
+else:
+    aliases["o"] = "xdg-open"