feat(save): Save a dataset with multiple file arguments

[dustmop]

No description provided.

[dustmop]

Fixes #690.

[b5]

Couple quick nits, this is looking really good!

[b5]

it's currently valid to also supply .html and .star files here directly. Relevant code that handles those extensions is still lib.ReadDatasetFile:

qri/lib/file.go

Lines 135 to 148 in b813d05

	case ".star":
	// starlark files are assumed to be a transform script with no additional
	// tranform component details:
	ds.Transform = &dataset.Transform{ScriptPath: path}
	ds.Transform.SetScriptFile(qfs.NewMemfileReader("transform.star", f))
	return
	case ".html":
	// html files are assumped to be a viz script with no additional viz
	// component details
	ds.Viz = &dataset.Viz{ScriptPath: path}
	ds.Viz.SetScriptFile(qfs.NewMemfileReader("viz.html", f))
	return

Any chance we can get cases that confirm both of those examples work? This is asking you to test code that I've written (😞), but we should confirm this behavior survives through this PR. The motivation is supplying no-configuration transform & viz components:

qri save --file transform.star me/dataset
qri save --file template.html me/dataset

I use both of these rather often, and find they make for easier tutorial writing.

[dustmop]

Added, along with an all-in-one combination of meta + transform + viz.

[b5]

Outdated comment. It'd be great if this function comment broke down some of the nuances of reading multiple filepaths into a dataset, keeping it as high-level as possible. Something like this (adjusting for accuracy):

// ReadDatasetFiles combines resources at zero or more filepaths, deserializing them into a
// *dataset.Dataset. Files can separately specify different components of a dataset
// but two provided components cannot overlap (modify the same component)

[dustmop]

Done.

[b5]

I'd prefer

func ReadDatasetFiles(pathList ... string) (*dataset.Dataset, error)

To me ReadDatasetFiles would be very useful when using qri-as-a-library by hiding the []string from the caller:

//  variadic arguments allows calls for easier single-file loading:
ds, err := lib.ReadDatasetFiles("./path.json")

//  and chaining that doesn't require []string allocation:
ds, err := lib.ReadDatasetFiles("./structure.json", "./meta.yaml")

[dustmop]

Good idea, this is much better.

[b5]

DOPE