Add compatibility info to project.toml

[radioflash]

Some Distributions versions (v0.21, v0.22, v0.23) were left out because the tests failed with them (on windows Julia 1.6)
All other listed versions worked (but not every permutation was tested).
Hyphens were not used in version specifications because those officially require Julia 1.4 or newer.

This version specification is stricter than the autogenerated one in the Julia package registry, but
this is reasonable:
The oldest (now declared compatible) dependency releases are from 2018 (older than this package itself).

[codecov-commenter]

Codecov Report

Merging #35 (ff46104) into master (1c4c2a2) will decrease coverage by 0.88%.
The diff coverage is n/a.

❗ Current head ff46104 differs from pull request most recent head 07c75fe. Consider uploading reports for the commit 07c75fe to get more accurate results

@@            Coverage Diff             @@
##           master      #35      +/-   ##
==========================================
- Coverage   81.63%   80.74%   -0.89%     
==========================================
  Files          12       12              
  Lines         343      296      -47     
==========================================
- Hits          280      239      -41     
+ Misses         63       57       -6     

Impacted Files	Coverage Δ
src/ukf.jl	87.80% <0.00%> (-1.09%)	⬇️
src/kf.jl	100.00% <0.00%> (ø)
src/ekf.jl	100.00% <0.00%> (ø)
src/gmphd.jl	100.00% <0.00%> (ø)
src/prune.jl	0.00% <0.00%> (ø)
src/utils.jl	50.00% <0.00%> (ø)
src/models.jl	83.33% <0.00%> (ø)
src/simulate.jl	100.00% <0.00%> (ø)
src/gmphd_classes.jl	100.00% <0.00%> (ø)
src/gmphd_extraction.jl	100.00% <0.00%> (ø)
... and 1 more

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[lassepe]

@radioflash Thank you again. What a great service 💪 We really should setup CompatHelper for this repository after this. One thing that has always bugged me is that, in the case of un-resolvable version constraints with other package, Julia will "figure out" that it can just use an older version of the package that does not have any compat entry at all (because, seemingly, that is compatible with all versions). Do you know how to work around that? Or is this not a problem anymore, now that everything has a "virtual" compat entry in the general registry?

[radioflash]

I've not encountered that problem myself so far (instead I often get dependencies stuck on old versions because some package is not listing the latest in its compat, even though it would work).

I think the introduction of the "virtual compat" entries in the registry prevents this, but I'm not 100% positive on that.

[lassepe]

@zsunberg do you know more about this?

[zsunberg]

I have encountered the problem that you talked about where it "upgrades" to an old version, but I am not sure if it is fixed by the registry virtual compat.

I would not worry too much about supporting old versions

[radioflash]

I have asked on the Julia slack, the problem is indeed gone:

Does the retroactive version capping prevent situations where Julia decides to use a (really old) package version without compat entries because it cannot resolve version conflicts otherwise? [...]

Kristoffer Carlsson:
That was the purpose of doing it, indeed

[lassepe]

Nice :) Thank you for the info!

[lassepe]

LGTM

[lassepe]

I will tag a new version on the coming weekend unless you have any objections, @jamgochiana