Returning `Interval` instead of tuples in distributions' Support members

[valbers]

• Fixes #292

This pull request introduces breaking changes.

Although these are just some small changes, they do represent breaking changes as the public contract of the Support members are changed. The Supports of the exponential distribution and of the discrete negative binomial have also been fixed (were previously closed intervals, but they should have the right side "open").

Check list

• [x] The project builds without problems on my machine

• [x] Adapted unit tests regarding the added features

[codecov-commenter]

Codecov Report

Merging #301 (3ae0bea) into developer (6014323) will increase coverage by 0.29%. Report is 6 commits behind head on developer. The diff coverage is 51.42%.

@@              Coverage Diff              @@
##           developer     #301      +/-   ##
=============================================
+ Coverage      46.31%   46.61%   +0.29%     
=============================================
  Files            148      148              
  Lines          16049    16182     +133     
  Branches        2176     2193      +17     
=============================================
+ Hits            7433     7543     +110     
- Misses          7968     7986      +18     
- Partials         648      653       +5     

Files	Coverage Δ
src/FSharp.Stats/Distributions/Continuous/F.fs	57.62% <100.00%> (+3.08%)	:arrow_up:
src/FSharp.Stats/Distributions/Continuous/Beta.fs	45.20% <0.00%> (ø)
src/FSharp.Stats/Distributions/Continuous/Chi.fs	26.08% <0.00%> (ø)
src/FSharp.Stats/Distributions/Continuous/Gamma.fs	56.38% <0.00%> (ø)
...FSharp.Stats/Distributions/Continuous/LogNormal.fs	8.00% <0.00%> (ø)
...rc/FSharp.Stats/Distributions/Continuous/Normal.fs	63.51% <0.00%> (ø)
.../FSharp.Stats/Distributions/Continuous/StudentT.fs	17.50% <0.00%> (ø)
...p.Stats/Distributions/Discrete/NegativeBinomial.fs	59.78% <0.00%> (ø)
...harp.Stats/Distributions/Continuous/Exponential.fs	0.00% <0.00%> (ø)
...ests/FSharp.Stats.Tests/DistributionsContinuous.fs	88.38% <55.55%> (-0.73%)	:arrow_down:

... and 4 files with indirect coverage changes