Support STAC 1.0 - part 0

[TomAugspurger]

This is a precursor PR to supporting STAC 1.0. It just updates the tests to use files from the PyStac repo, rather than sat-stac.

A followup PR will update the URLs to point to the STAC 1.0.0 versions of those files while updating the code to use PyStac 1.0.

The first two commits are just #94 and can be ignored. fbf84a2 has the actual changes.

[scottyhq]

Thanks for starting this @TomAugspurger ! I left some comments trying to figure out whether to use external examples for testing, or if we might want to put our own example STAC=1.0 examples in this repository (with valid asset / subcatalog links)

[TomAugspurger]

I think having our own STAC catalogs, with just the data we need for testing, makes sense. Now that we're at STAC 1.0, this seems more feasible. I'll look into that.

[TomAugspurger]

OK, updated to use some local files, rather than opening STAC objects from remote URLs.

I think the stack_bands might be a bit under-tested, but hopefully I got it right. The items I'm using came from the Planetary Computer, so URLs to data files in blob storage have to be signed to download. I don't think we want to do that in our unit tests, but here's a manual tests:

In [1]: import rasterio

In [2]: import pystac, planetary_computer, intake

In [3]: item = planetary_computer.sign_assets(pystac.read_file("https://planetarycomputer.microsoft.com/api/stac/v1/collections/sentinel-2-l2a/items/S2B_MSIL2A_20210610T115639_N0212_R066_T33
   ...: XWC_20210613T190000.SAFE"))

In [5]: intake_item = intake.open_stac_item(item)

In [6]: ds = intake_item.stack_bands(["B02", "B03"])().to_dask()

In [7]: ds
Out[7]:
<xarray.DataArray (band: 2, y: 10980, x: 10980)>
dask.array<concatenate, shape=(2, 10980, 10980), dtype=uint16, chunksize=(1, 10980, 10980), chunktype=numpy.ndarray>
Coordinates:
  * band     (band) int64 1 1
  * y        (y) float64 8.3e+06 8.3e+06 8.3e+06 ... 8.19e+06 8.19e+06 8.19e+06
  * x        (x) float64 5e+05 5e+05 5e+05 ... 6.098e+05 6.098e+05 6.098e+05
Attributes:
    transform:      (10.0, 0.0, 499980.0, 0.0, -10.0, 8300040.0)
    crs:            +init=epsg:32633
    res:            (10.0, 10.0)
    is_tiled:       1
    nodatavals:     (nan,)
    scales:         (1.0,)
    offsets:        (0.0,)
    AREA_OR_POINT:  Area

[scottyhq]

Looks great @TomAugspurger ! Would be happy to merge this as is. We can add some additional tests in future PRs and hopefully release 1.0.0 shortly after pystac 1.0.0 ?

[TomAugspurger]

Yeah, releasing shortly after pystac 1.0 is my hope.