in reader macro expansions, set position of generated symbol to position of original punctuation mark (which is also the position of the newly generated list)
remove leaf from ast, replace its uses with a one-elem struct
whoops, miscounted args to set-bang
token AST: do not bother having a 'tree' sub-node, just put all properties on the same node.  also remove some needless inconsistencies
ditch obsolete code