Add ptemcee sampler

Adds the ptemcee sampler and some useful methods to the parent Sampler class. Note - ptemcee is a derivative of emcee but with parallel tempering. (originally parallel tempering was implemented into emcee, but has since been removed in the latest version as the maintainer felt it was too much of a burden).

added 27 commits

• 1c879b8c...9f7b92d1 - 26 commits from branch master
• 5eb0c97e - Merge branch 'master' into 'add-ptemcee-sampler'

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I resolved a conflict with master. This looks good.

If this is ready, I'm happy to merge.

Actually, can you add the appropriate requirement(s) for this sampler.

added 73 commits

• 5eb0c97e...39a95683 - 65 commits from branch master
• aa8f6018 - Merge branch 'master' into add-ptemcee-sampler
• b474c434 - Further improvements to emcee implementation
• 3cffb6e0 - Merge branch 'master' into add-ptemcee-sampler
• 964f8c23 - Further minor improvements to ptemcee implementation
• 86fbbdbf - Merge branch 'master' into add-ptemcee-sampler
• b766f6d3 - Add dynesty and fix ptemcee bugs after merge
• 75c5f686 - Merge branch 'add-ptemcee-sampler' of git.ligo.org:Monash/peyote into add-ptemcee-sampler
• e2846e7a - Minor update to comparison

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added 1 commit

• 57ae694a - Add ptemcee to requirements

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added 1 commit

• b41c6c2a - Remove switching mass_1 and mass_2 from the random draw

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enabled an automatic merge when the pipeline for b41c6c2a succeeds

mentioned in commit de5116ed

merged