new: Make a table into a tree
  t: table
returns
  tr: tree
__index: Tree __index metamethod
  tr: tree
  i: non-table, or list of indices {i1 ... in}
returns
  v: tr[i]...[in] if i is a table, or tr[i] otherwise
__newindex: Tree __newindex metamethod
Sets tr[i1]...[in] = v if i is a table, or tr[i] = v otherwise
  tr: tree
  i: non-table, or list of indices {i1 ... in}
  v: value
clone: Make a deep copy of a tree, including any
metatables
  t: table
  nometa: if non-nil don't copy metatables
returns
  u: copy of table