Added system<<components macro for cleaner init of entities.

See usages for how to use, but basically pass the system and entity,
and a vector of vectors containing the keyword name of the component
and the map for the map->Comp constructor.
EG: (system<<components system e-this [[:item {:pickup-fn
pickup-item}][:torch {:brightness 2}][:broadcaster {:msg-fn (constantly
"a torch")}]]