Feature: Add a setting for unsorted listing

[svoop]

While many like the structure view to list the matches sorted by type and name, others prefer to see the matches unsorted in the order of appearance in the document.

For ctags, adding -u to the command arguments will do the trick.

Thanks for considering this feature.

(Btw, I've just submitted a PR #22 to add support for RSpec and MiniTest which makes much more sense if you can switch off sorting.)