Use specific env variables

[rkrug]

The code now checks if the environmental variables

- ZENOODO_TOKEN
- ZENODO_SANDBOX_TOKEN
- FIGSHARE_TOKEN

are set and reads these. If they are not set, it uses the heuristic algorithm included before.

[Rafnuss]

Nice, this quite an annoying missing piece in the documentation. Can I ask why not using keyring? Seems like it's quite popular to manage such token? Or maybe not?

[mpadge]

@Rafnuss Main reason that credential-management systems are not used here is because they are often difficult to use within containerized environments such as Dockerfiles. Direct use of environment variables offers greater flexibility for using this package in a range of computational environments.

And @rkrug sorry that I forgot about this PR. You still interested in moving ahead with it?

[rkrug]

No worries.

Yes please - I am not using deposits at the moment, but I will use it again. And using these specific names for the end variables would make the handling more robust.

[mpadge]

Thanks @rkrug, and apologies again for leaving this hanging so long. With that minor improvement, it should be good to merge.

[mpadge]

Suggested change

	if (e == "") {
	if (!nzchar (e)) {