Add filter on tag player.target

Now we can specify a npc/<entity>/<entity.type> as target.
few examples
<p@player.target[npc] will target only npc
<p@player.target[player] will target only npc
<p@player.target[e@123|e@321|zombie] will target only entity 123 or 321
or zombie
Merge pull request #557 from blankiito/master

Add filter on tag player.target