Fixed: echo does not work with double-quoted strings

After you made your guess about what the problem was, it suddenly occurred to me that I had seen some code in the parser that might handle this very scenario... and then I realized that of course you already had the problem solved and all I had to do was plug it into the `:echo` command.

This removes the annoying case that `:echo` was treating double-quoted strings as comments, i.e. `:echo "foo"` was processed like plain old `:echo`. (*Note*: according to Vim documentation, comments after echo should be done thus: `:echo "foo" | "my comment`, though that does not yet work in VsVim.)