Add --extra-args option

[cl3to]

Users can now pass additional arguments in the CLI. These arguments can be used within the command template in the spinner's YAML configuration. The --extra-args parameter accepts a list of key=value pairs, separated by semicolons.

Exemple:

host_list=$(scontrol show hostname "$SLURM_JOB_NODELIST" | tr '\n' ',' | sed 's/,$//')
images_dir="/images"
spinner -c mpich.yaml -r --extra-args 'hosts=$host_list;images=$images_dir'

Closes #20

[rodrigo-ceccato]

LG, only two comments:

1. Please update the example in: docs/slurm.MD
2. It would be cool to have it in the CI (and in /docs/examples)

metadata:
  description: Sleep check
  version: "1.0"
  runs: 1
  timeout: 5
  retry: True
  retry_limit: 0

  sleep_test:
    command:
      template: >
        sleep {{sleep_ammount + (extra_time | int)}}

sleep_test:
  sleep_ammount:
    - 1
    - 2

that could be ran with:
spinner -r -c extra_args.yaml --extra-args=extra_time="4"

Overall, I like this new CLI a lot

[cl3to]

@rodrigo-ceccato,

I've updated the PR based on your suggestions.

One thing to note: the extra arguments are currently only included in the metadata, not in the final dataframe. We can address this later when we revise the YAML template and other related elements.

[rodrigo-ceccato]

LGTM!

Metadata from CLI not being propagated to the Dataframe is a problem IMO, because our model is simpler if we can treat both executions as the same thing (i.e. it behaves the same if the data come from --extra-args or if comes from the YAML fields).

But I do agree that it would be better to fix thsi after PR#40 merges.

What do you think @leiteg ?