Separate .trees and .treebank, and add a script for making the latter from the former

testsuite/lpgf/mkTreebank.sh

@@ -0,0 +1,10 @@
+#!/usr/bin/env bash
+set -e
+if [ $# -lt 1 ]; then
+  echo "Must specify trees file"
+  exit 1
+fi
+ABSNAME="${1%.*}"
+echo "read_file -file=$1 -lines -tree | linearize -treebank | write_file -file=$ABSNAME.treebank" | gf --run $ABSNAME*.gf
+echo "Wrote $ABSNAME.treebank"
+echo "(you will have to add newlines separating the trees manually)"