[caprieval] comparisons against multiple references

[VGPReys]

Checklist

• Tests added for the new code
• Documentation added for the code changes
• Does not break licensing
• Does not add any dependencies, if it does please add a thorough explanation

Summary of the Pull Request

This PR in made to handle comparisons with multiple references.

This is performed by turning on the parameter multiple_references = true (default false).
In this scenario, reported values in capri_ss.tsv are the ones obtained against the best reference.

If multiple_references = false (default), the first reference will be used as reference.

I had to add the __eq__ and __lt__ methods to the CAPRI class, so comparisons could be performed by functions/methods such as sorted([CAPRI, CAPRI]) or [CAPRI, CAPRI].sort().

Related Issue

#1133