Add option to compute relative ESS

[sethaxen]

Fixes #80 by adding a convenience keyword relative=false to ess and ess_rhat.

[github-actions]

Pull Request Test Coverage Report for Build 4714877976

• 5 of 5 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.008%) to 96.556%

---

Totals
Change from base Build 4399022657:	0.008%
Covered Lines:	813
Relevant Lines:	842

---

💛 - Coveralls

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (f2aca2d) 96.54% compared to head (8d46fec) 96.55%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #81   +/-   ##
=======================================
  Coverage   96.54%   96.55%           
=======================================
  Files          10       10           
  Lines         840      842    +2     
=======================================
+ Hits          811      813    +2     
  Misses         29       29           

Impacted Files	Coverage Δ
src/ess_rhat.jl	100.00% <100.00%> (ø)

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[devmotion]

Looks good to me.

[coveralls]

Pull Request Test Coverage Report for Build 4714915466

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 5 of 5 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.008%) to 96.556%

---

Totals
Change from base Build 4399022657:	0.008%
Covered Lines:	813
Relevant Lines:	842

---

💛 - Coveralls