Add support for “self-identification”

[smondet]

This fixes #213.

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This change is

[ihodes]

This might be nicer to match with downstream as just Self_identification of string instead.

We could also use a type instead. If we used a type instead of a string, Merlin/the compiler could help us figure out what we can match on. As it is, someone will have to go through the source code to figure out what they can match on (and it could change/break on them in the future without a warning).

(Still not sure, even with the Hamkepi PR, that this solution is as simple for the user as passing ?requirements down from the tool itself…)

[smondet]

It would be very annoying to manage:

• the ?requirements (the argument needs to go up the stack very far, you would end-up with Gatk.indel_realigner that takes tons of overriding arguments: ?gatk_requirements, ?samtools_sort_requirements, ?samtools_index_requirements, ?merge_bams_requirements, etc. (installations, downloads, …)
• and then it would have to go up the Pipeline_edsl API too

And on top of that it would break the clean-ish separation between bioinformatics and infrastructure. The goal is to be able to reuse 100% of the pipeline/Tools code unchanged, and switch between completely different Machine.ts at will.

[ihodes]

Another downside: if you have different invocations of the same tool, you can't configure them separately.

[ihodes]

Tough to name this, but instead of ~self_ids, we could just have ~ids (as it is the ID of the make process), and the type in ~requirements could be ``Make_process_id`?

(I can file this as a separate issue)