Update to 0.4.0 - adding mosaic support

[nimne]

Merge from dev branch. Changes as outlined in the readme:

• Added support for tiled images
  • m was added as a new dimension (for tiled images)
  • LifImage changes:
    • New get_iter_m() function
    • New mosaic_position attribute with (FieldX, FieldY, PosX, PosY)
• Under the hood changes
  • LifImage.dims is now a named tuple for clearer code
• Other things
  • Prettier outputs for repr()
  • Switch to github CI