Update to b and u events as well as dlPost

Changed Post / group.pArray generation:
     The Post.pid is automatically added now and is either set as the correct pid if it's in the group.pQueue or to None if it's not.

Added the group.dQueue:
     If the group.dlPost method is used and the post has a Post.pid == None then it will append to this array. When the Digest.u event is received it checks if the Post.pnum is in this Queue and sends the delmsg command if it does.

Added the group.rQueue:
    The Digest.deleteall and Digest.delete methods will append the Post.pid to this queue if there is no matching Post in group.pArray. When the Post.pid is sent to Digest.u it will instead of processing normally remove the Post from the group.pArray.