Add fit mle weighted laplace

[dmetivie]

I added fit_mle(Laplace, x, w) method using the weighted median plus a test in the test section of Laplace fit.

[codecov-commenter]

Codecov Report

Base: 83.60% // Head: 85.60% // Increases project coverage by +1.99% :tada:

Coverage data is based on head (d5e4f6c) compared to base (c431d20). Patch coverage: 88.88% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1676      +/-   ##
==========================================
+ Coverage   83.60%   85.60%   +1.99%     
==========================================
  Files         130      130              
  Lines        6642     8189    +1547     
==========================================
+ Hits         5553     7010    +1457     
- Misses       1089     1179      +90     

Impacted Files	Coverage Δ
src/univariate/continuous/laplace.jl	94.52% <88.88%> (-0.03%)	:arrow_down:
src/genericfit.jl	66.66% <0.00%> (-8.34%)	:arrow_down:
src/univariate/continuous/rician.jl	94.87% <0.00%> (-1.85%)	:arrow_down:
src/univariate/discrete/bernoullilogit.jl	12.00% <0.00%> (-1.64%)	:arrow_down:
src/univariate/continuous/arcsine.jl	88.88% <0.00%> (-1.44%)	:arrow_down:
src/samplers/poisson.jl	90.78% <0.00%> (-1.40%)	:arrow_down:
src/multivariate/mvlognormal.jl	93.02% <0.00%> (-0.73%)	:arrow_down:
src/multivariates.jl	44.82% <0.00%> (-0.63%)	:arrow_down:
src/univariates.jl	74.54% <0.00%> (-0.59%)	:arrow_down:
src/matrix/matrixnormal.jl	94.11% <0.00%> (-0.53%)	:arrow_down:
... and 113 more

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[dmetivie]

Thanks for the review, I'll do your suggestion and test, when I find some time.

Do you have a citation for this being equivalent to the MLE of a Laplace distribution?

I was going to write down the proof because I don't see it written explicitly anywhere.

[ParadaCarleton]

I was going to write down the proof because I don't see it written explicitly anywhere.

Yeah, I think it's a well-known enough result that we can use it. (The proof should be identical to the one for the unweighted case).