Submodule plots is in `__all__` but not imported in `__init__.py`

Hi,

This might be deliberate but it seems that the submodule plots is not imported in the __init__.py but is included in __all__.
I can see there are some optional dependencies for some of the functions but their imports are only inside the concerned functions.

That means that if someone wants to use the plots submodule they would need to explicitly import it, which seems a bit strange when the documentation has this:

import cmocean
cmocean.plots.plot_gallery()

Which currently gives:

AttributeError: module 'cmocean' has no attribute 'plots'

package init.py から始め、plots に対する all エントリをドキュメントに記載された import 例と比較します。import cmocean に続けて cmocean.plots.plot_gallery() を実行したときの現在の動作を確認します。ドキュメントに記載されたアクセスで AttributeError が発生しなくなれば完了です。