rsi 0.3.0

• rsi has been peer-reviewed by the rOpenSci project! Huge thank you to
  @OldLipe and @mdsumner for their extremely helpful reviews.

• sentinel2_mask_function() now masks out SCL values of 2, "DARK_AREA", by
  default.

• landsat_mask_function() gains an argument, masked_bits, that allows you
  to specify the values you wish to mask out by bit values rather than just
  integers. Refer to the Landsat science product guide for further information
  on what bit values represent for your platform of interest.

• get_stac_data() no longer fails if downloading an asset fails, but instead
  returns a raster with all available data. This may still fail when a single
  asset fails to download while downloading multiple assets combined within a
  single raster; please open an issue if this happens to you! Thanks to
  @laurenkwick in #74 (#75).