Rename

[ThijsvdLaar]

This PR implements some important renaming conventions for improved accuracy and compactness

• ProbabilityDistribution -> Distribution
• Aliases P for Distribution and M for Message
• Nonlinear -> Delta
• GaussianMeanPrecision -> Gaussian{Precision}
• GaussianWeightedMeanPrecision -> Gaussian{Canonical}
• GaussianMeanVariance -> Gaussian{Moments}
• Gaussian defaults to Gaussian{Moments}
• Convert all demos to work with Plots

[codecov-commenter]

Codecov Report

Merging #193 (e965127) into master (dc808ac) will increase coverage by 0.02%.
The diff coverage is 88.82%.

@@            Coverage Diff             @@
##           master     #193      +/-   ##
==========================================
+ Coverage   87.16%   87.19%   +0.02%     
==========================================
  Files          97       97              
  Lines        4614     4614              
==========================================
+ Hits         4022     4023       +1     
+ Misses        592      591       -1     

Impacted Files	Coverage Δ
src/engines/julia/update_rules/sample_list.jl	100.00% <ø> (ø)
src/factor_nodes/clamp.jl	94.44% <ø> (ø)
src/factor_nodes/transition_mixture.jl	95.65% <ø> (ø)
src/update_rules/beta.jl	100.00% <ø> (ø)
src/variable.jl	93.90% <ø> (ø)
src/engines/julia/update_rules/beta.jl	29.03% <33.33%> (ø)
src/engines/julia/update_rules/dirichlet.jl	50.00% <50.00%> (ø)
src/factor_nodes/sample_list.jl	75.60% <63.33%> (ø)
src/algorithms/structured_variational_bayes.jl	94.25% <66.66%> (ø)
src/factor_nodes/contingency.jl	87.50% <71.42%> (ø)
... and 64 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update dc808ac...e965127. Read the comment docs.

[ThijsvdLaar]

Renaming appears complete, will merge, thanks @abpolym for checking