Homogenize API arguments

[atedstone]

This PR causes breaking changes to API

Resolves the rest of #432.

• Remove dst_
• Replace rst with raster
• grid_size to size
• The various forms of sample (see below)
• Always use points, never pts

Grammar of sampling

This PR proposes to regularise the grammar around the word sample and its derivatives.

• When the intention is to return a (random) sample, the term sample is used. Previously, subset or subsample were both used to denote this purpose.
• downsample or upsample defines a change in a Raster's resolution. The more generic term is resample, but the use of a specific direction is preferred. Try not to use resample as this has connotations of towards reproject.
• The terms subset and subsample refer to an contiguous portion of data (e.g. an x*y window of a Raster, specific bands of a Raster, or row n...row m of a Vector), without a change in resolution. I am regularising to subset.

[rhugonnet]

Thanks @atedstone, this is great!! I didn't find anything to comment on in the code changes.

I like the homogenization to sample and differentiation with subset! 😄
It looks like subset is used only in split_bands, we could even rename into something specific to that function like bands to avoid any kind of confusion?

[adehecq]

Nice work !
As discussed on slack, I find that removing the dst_ prefix everywhere makes sense from a user/API point of view, but it may be a bit less easy to read the code. We'll see!
I find that size is not clear enough. I would favor grid_size to clarify that we're talking about the dimensions of the array. But we can revert in a future PR if we all agree.

[adehecq]

It looks like subset is used only in split_bands, we could even rename into something specific to that function like bands to avoid any kind of confusion?

For consistency, we could use the same terminology as in load which is indexes. Although I'm not a huge fan of that term, I always forget the name...

[atedstone]

I also don't find indexes that intuitive. From the xarray side of life, index can be along any dimension. How about the keyword band/bands instead, for both load() and split_bands()?

[adehecq]

I also don't find indexes that intuitive. From the xarray side of life, index can be along any dimension. How about the keyword band/bands instead, for both load() and split_bands()?

I would be fine with bands. But this would just be undoing what was done in a previous PR: #346. Any thoughts @rhugonnet ?

[rhugonnet]

+1 for grid_size and for bands!