lemmas; headmarked binarization; read/write trees from stdin/out

- runexp: fix bug which caused evaluation with deleted POS tags to fail
- treebank: option to add lemmas to trees when reading treebank
- treetransforms: option to prepend head label to list of horizontal
  siblings; e.g., NP|<NN;JJ> where immediate sibling is JJ, head is NN
- treetransforms: read/write the stdin/out if no filename is given