Improved HDI computation

[arossia94]

Improved computation of HDIs with variation of confidence level and reporting several disjoint intervals and the peak of the distribution inside each interval.

Changes and improvements:

• HDIs computed with different confidence levels.
• Better reporting of disjoint HDIs.
• Computation and reporting of the 1st mode inside each disjoint interval.
• Computation of monomodal HDIs.
• Option in the report runcard to use multimodal or unimodal HDIs.
• Fix the spider plot
• Add instructions and examples in the docs.

[LucaMantani]

Could you add an example on how to obtain these bounds in the report, if any new option is available in the card, etc

[arossia94]

@jacoterh , when you have time, could you take a look at the spider plot function here? Somehow it broke down but I have no idea why.

[arossia94]

The spider plot is working now, but requires more thorough testing.

[arossia94]

The module coefficients_utils.py needs a deep restructuring to pass the CodeFactor check.
In particular, we could move the internal part of write_cl_table and some of the functions inside the class CoefficientsPlotter to a separate module (even perhaps that whole class...).