Added tox.ini posargs option, you can pass arguments to unit tests

https://stackoverflow.com/questions/35697353/how-to-run-only-one-test-in-tox

Added .tox to .gitignore (to use tox locally)

Fix misspelling on lark/lark.py documentation

Trimmed whitespaces and ensured a new line on the end of the file

number add BIN_NUMBER

Without BIN_NUMBER, the following error occurs:
lark.exceptions.UnexpectedCharacters: No terminal defined for 'b' at line 1 col 2

0b10
 ^

Fix typo in docs

Instructions how to get Shift/Reduce messages printed (Issue #258)

Method iter_subtrees_topdown added

Allow to passing "rankdir" to lark/tree.py:pydot__tree_to_png

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

docs: clarify end_column value

I interpreted "the column where the token ends" to mean "a pointer
to the last character in the token", which would be the same as
the start column for a single-character token.

However, that's not what lark actually reports. Reword to clarify
this.

https://github.com/lark-parser/lark/issues/240

Added missing binary files to .gitignore