- Create a wop class
- Move all the variable tools to level.variables
- Add ast to level.variables to parser variables that we need

Tools that allows to expand string and subsitute variables.

default dict add missing keys.
SO says that we can override the __missing__ method, but this works.

- Add nammed objects
- Add the exit as a nammed object
- Update code format
- Fix box in the curses level

- small refactoring
- update main infinite look

- Update player character rep according to its direction.
- Fix init with empty string
- Handle attribute error, so a non fully fetched variable do not
raise an exception.

We cannot add attributes to a method, and I do not want to wrap the
callback function or to modify the callback function set, so I
moved the check to the runtime. It should not change the performance.

- Allow two types of callback functions: 1 and 2 arguments. Functions
The variable's name is given before the the value if the a function that
takes 2 arguments in given.

- the file `level.py` starts to be really huge.
So I splitted it into 4 parts.
- update formating on `utils.py` and `arcade_ui.py`

Add the variable name to value_change events so we can use
a single handler to handle a set of variables.

Add API for game engine + Easytracker wrapper to record and replay inputs

See merge request !3