Tidy up RST parser slightly, add rudimentary tests
Include rst_dt stuff in the documentation
RST treebank API tweak: make RSTTree a Tree
Represent RST treebank trees as educe Standoff
Avoid accidental commit of copyrighted files
Move RST test strings into test module
RST set_origin

Duck-typing our way into looking like annotations
RST: change text behaviour (see long comment)

- support trees that don't have <EDU></EDU> tags
- insert some whitespace (a single newline) between
  EDU text for standoff mode