Support simultaneous keys of 3 or more

[lizyn]

When setting <from> to simultaneous keys as combination of more than two keys (in simple syntax, e.g. [:a :b :c]), goku 0.2.9 yield error messages:

ERROR: invalid <from> in main section's XXX(rule description)
Failed!

I know that most Apple keyboards have only "2-key rollovers", but a number of three-key-combo or 4-key-combo, etc. can still be recognized by certain keyboards. And karabiner.json supports that syntax, so I think it's reasonable to adjust this behavior.

[narze]

It works if you use :rules format I've tried 4 sim keys

{:des "SuperDuper <- S+D" :rules [:!qmk [{:sim [:s :d]
                                     :simo {:interrupt true
                                            :dorder :insensitive
                                            :uorder :insensitive
                                            :afterup {:set ["superduper-mode" 0]}}} {:set ["superduper-mode" 1]}]]}
        {:des "A+S+D -> SD+Option" :rules [:!qmk [{:sim [:a :s :d]
                                     :simo {:interrupt true
                                            :dorder :insensitive
                                            :uorder :insensitive
                                            :afterup {:set ["superduper-mode" 0]}}} [{:set ["superduper-mode" 1]} :left_option]]]}
        {:des "A+S+D+F-> SD+Delete word" :rules [:!qmk [{:sim [:a :s :d :f]
                                     :simo {:interrupt true
                                            :dorder :insensitive
                                            :uorder :insensitive
                                            :afterup {:set ["superduper-mode" 0]}}} [{:set ["superduper-mode" 1]} :!Odelete_or_backspace]]]}

[yqrashawn]

fixed in v0.3.0