Tiler module

[lillythomas]

Tiling module that generates 256x256 tiled xarray datasets from the larger scene-level datacube generated in datacube.py.

To do:

• add cloud filter
• refine extent to tile within to valid data region
• add main script to call the datacube module followed by the tile module
• decide on method for storing the tiled xarray datasets
• add some docstrings