initial add of xpath stuff
working on xpath
tweak
add getChildren() method to Tree.
oops; need method: add getChildren() method to Tree.
refine getChildren() method to narrow return type.
adding more xpath expr types
stash
stash
got a draft implementation
got test rig start. added support test rig stuff to exec parser. add findAll to ParseTree interface.
cleaned up test rig. more tests. fix bugs.
simplify
prototype xpath
rebuilt XPath using ANTLR itself; added error handling; added ! operator
rm comment
rm unneeded getChildren
rm comments
mv findAll to XPath; rm old test in playground.
add antlr4 to build.xml