drop tinker interface from this repo;

the canonical interface source is at https://github.com/ggrov/tinker/blob/45cadf637e812f4b87995574b9499b40530ee9da/src/parse/whym_tree.ML (as of this commit)
updated PP-to-Tinker encoding;

Use graph representation of PP for clearer conversion algorithm
cleanup/streamline old code
multiple selection util method
support exporting proof
encode labels just in case
Merge branch 'tinger-integration'