matplotlib is not specified as dependency when it should

[limdor]

matplotlib is imported in https://github.com/ipython/matplotlib-inline/blob/0.1.7/matplotlib_inline/backend_inline.py#L6
However, it is not specified in https://github.com/ipython/matplotlib-inline/blob/0.1.7/pyproject.toml#L30

[martinRenou]

This was done on purpose, adding matplotlib as a dependency would make it a sub-dependency of IPython, which is not something we want.

It's true though that those direct imports should probably not be done, we should move those imports as lazy imports inside the functions of the inline backend.

This was never a problem an IPython since IPython lazily imports matplotlib_inline already