nilearn.exceptions: Exceptions and warnings

Custom warnings and errors used across Nilearn.

Warnings

MaskWarning	Custom warning related to masks.
NotImplementedWarning	Custom warning to warn about not implemented features.

Exceptions

AllVolumesRemovedError()	Warns the user if no volumes were kept.
DimensionError(file_dimension, ...)	Custom error type for dimension checking.
MeshDimensionError([msg])	Exception raised when meshes have incompatible dimensions.

        classDiagram
  BaseException <|-- Exception
  Exception <|-- AllVolumesRemovedError
  Exception <|-- TypeError
  Exception <|-- ValueError
  Exception <|-- Warning
  TypeError <|-- DimensionError
  UserWarning <|-- MaskWarning
  UserWarning <|-- NotImplementedWarning
  ValueError <|-- MeshDimensionError
  Warning <|-- UserWarning