Update interval type

[bvenn]

Closes #286

Please list the changes introduced in this PR

• addition of open and half open intervals
• rename Intervals to Interval and shrink to FSharp.Stats.Interval.createClosed instead of FSharp.Stats.Intervals.Interval.create
• A check whether the interval minimum is lower than the interval maximum was not implemented because of the reasons discussed in #286. Briefly, in three dimensional space [1,2,3] < [2,1,3] returns true despite it beeing an invalid interval in the second dimension.

[Required] please make sure you checked that

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

[Optional]

• [x] Added unit tests regarding the added features

[codecov-commenter]

Codecov Report

Merging #287 (480a9b9) into developer (7de8b82) will decrease coverage by 0.57%. Report is 1 commits behind head on developer. The diff coverage is 27.85%.

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@@              Coverage Diff              @@
##           developer     #287      +/-   ##
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- Coverage      47.93%   47.36%   -0.57%     
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  Files            148      148              
  Lines          15767    15884     +117     
  Branches        2063     2159      +96     
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- Hits            7558     7524      -34     
- Misses          7622     7708      +86     
- Partials         587      652      +65     

Files Changed	Coverage Δ
src/FSharp.Stats/Array.fs	2.53% <0.00%> (ø)
src/FSharp.Stats/Distributions/Bandwidth.fs	3.27% <0.00%> (ø)
...Sharp.Stats/Distributions/Continuous/ChiSquared.fs	72.72% <0.00%> (ø)
...harp.Stats/Distributions/Continuous/Exponential.fs	0.00% <0.00%> (ø)
...c/FSharp.Stats/Distributions/Continuous/Uniform.fs	0.00% <0.00%> (ø)
...c/FSharp.Stats/Distributions/Discrete/Bernoulli.fs	48.83% <0.00%> (ø)
...rc/FSharp.Stats/Distributions/Discrete/Binomial.fs	50.94% <0.00%> (ø)
...arp.Stats/Distributions/Discrete/Hypergeometric.fs	77.19% <0.00%> (ø)
src/FSharp.Stats/Distributions/Discrete/Poisson.fs	58.73% <0.00%> (ø)
src/FSharp.Stats/Distributions/KernelDensity.fs	0.00% <0.00%> (ø)
... and 10 more