Add plotting via Makie as Extension

[alecloudenback]

Current Status:

A color-blind-friendly color scheme (:tol_vibrant) is used to plot the trance and parameter densities for each parameter in each chain.

Sample plots:

Basic Layout

Large number of parameters

Large number of chains

To-do

• [ ] Documentation
• [ ] Tests (test that plot gets created for a variety of sizes?)
• [ ] Extend Makie.plot instead of a new myplot function (not good idea)
• [ ] Gracefully handle more than 7 chains for the color scheme

Sample Script

julia> using MCMCChains, CairoMakie
julia> chns = Chains(randn(300, 5, 3), [:A, :B, :C, :D, :E]);
julia> myplot(chns)

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 5.12821% with 37 lines in your changes missing coverage. Please review.

Project coverage is 81.90%. Comparing base (5f8e591) to head (20e76a4).

:exclamation: Current head 20e76a4 differs from pull request most recent head 1144212

Please upload reports for the commit 1144212 to get more accurate results.

Files	Patch %	Lines
ext/MCMCChainsMakieExt.jl	0.00%	37 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #454 +/- ## ========================================== - Coverage 84.70% 81.90% -2.80% ========================================== Files 20 21 +1 Lines 1072 1111 +39 ========================================== + Hits 908 910 +2 - Misses 164 201 +37 ```

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[alecloudenback]

After talking with the Makie devs on Discord:

• The convert_arguments isn't really a path because all it will do is be able to plot the data into a single plot (no faceting by parameter or chain) or convey metadata (e.g. parameter name or chain number)
• Recipes are for creating a single sub-plot, not defining a figure with multiple sub-plots as desired
• The recommendation was to just define a new function that would plot as desired (e.g. trace(chains)). Adding a new method to plot isn't well defined or supported by Makie.

The latest commit is the recommended approach, including registering an error hint if a Makie-related package isn't yet loaded and trace is called.

[alecloudenback]

@devmotion / @theogf pinging since you had some initial feedback requesting a recipes-based approach, but I don't think that works when wanted to plot multiple chains/parameters (see my last post). If good with the overall approach here, I can knock out the remaining To-Dos.