Make bat_marginalize return namedtuple

[Cornelius-G]

Fix of issue #132

[codecov-commenter]

Codecov Report

Merging #133 into master will decrease coverage by 0.04%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master     #133      +/-   ##
==========================================
- Coverage   30.25%   30.21%   -0.05%     
==========================================
  Files          69       69              
  Lines        3662     3667       +5     
==========================================
  Hits         1108     1108              
- Misses       2554     2559       +5     

Impacted Files	Coverage Δ
src/plotting/MarginalDist.jl	0.00% <0.00%> (ø)
src/plotting/recipes_MarginalDist_1D.jl	0.00% <0.00%> (ø)
src/plotting/recipes_prior.jl	0.00% <ø> (ø)
src/plotting/recipes_samples_1D.jl	0.00% <ø> (ø)
src/plotting/recipes_samples_2D.jl	0.00% <ø> (ø)

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