Add:
- missing imports
- __version__ variable

Additionally regenerated json parser example

Using OrderedDict provides these properties:
- given subtree is yielded only once since it's stored in OrderedDict
only once (even though it may be put there multiple times) so no need
to double check if subtree was already seen
- order of iteration is preserved as it was previously when subtrees
to iterate over were stored in a list

Keeping the explicit `rankdir="LR"` as default, add `kwargs`
to `pydot__tree_to_png` and `pydot.Dot` so that all graphviz
attributes are available for the graph.

lark/tree.py

shaping. For example, passing "TB" instead of "LR" makes the tree
to be draw vertically instead of horizontally.

https://stackoverflow.com/questions/29003465/pydot-graphviz-how-to-order-horizontally-nodes-in-a-cluster-while-the-rest-of-t

* All exceptions are now under exceptions.py
* UnexpectedInput is now superclass of UnexpectedToken and UnexpectedCharacters,
  all of which support the get_context() and match_examples() methods.

Nearley tool still needs fixing

It emulates antlr's visitor behavior for a dynamic evaluation order of subtrees

When a tuple is passed as the argument to percent-formatting, its
elements are interpreted as multiple arguments. The pretty printer
previously passed tuples (e.g. those introduced via a Transformer) from
the tree directly to the percent operator, causing a TypeError because
the format string only calls for a single argument. This fix simply
wraps the argument in a one-tuple to ensure it is not interpreted as
multiple arguments if it itself is a tuple.