Convergence Logging

[mileslucas]

Fixes #27

Here's what I've got started in terms of convergence logging. I'd really like this feature and want to help get it done. Unfortunately, I have extremely little macro knowledge so I haven't dived into that. I would fully appreciate contributions to this regard.

This design is basically what @tkf wrote out in this comment. I've mimicked some of the code for the Progress struct and can get the following behavior:

julia> using ProgressLogging: Convergence, Ascending, Descending
julia> using UUIDs: UUID
julia> print(Convergence(UUID(1); values=[12, 13], thresholds=[5, 5]))
Convergence: 12.0|5.0
Convergence: 13.0|5.0

julia> print(Convergence(UUID(1); values=[12, 13], thresholds=[5, 5], directions=fill(Ascending, 2), step=4))
4 Convergence: 12.0↑5.0
4 Convergence: 13.0↑5.0

julia> print(Convergence(UUID(1); values=[12, 13], thresholds=[5, 5], directions=fill(Descending, 2)))
Convergence: 12.0↓5.0
Convergence: 13.0↓5.0

julia> print(Convergence(UUID(1); values=[12, 13]))
Convergence: 12.0|??
Convergence: 13.0|??

julia> print(Convergence(UUID(1); names=["A", "B"]))
A: ??|??
B: ??|??

[codecov-commenter]

Codecov Report

Merging #32 into master will decrease coverage by 9.35%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master      #32      +/-   ##
==========================================
- Coverage   69.04%   59.69%   -9.36%     
==========================================
  Files           1        2       +1     
  Lines         168      196      +28     
==========================================
+ Hits          116      117       +1     
- Misses         52       79      +27     

Impacted Files	Coverage Δ
src/ProgressLogging.jl	69.23% <ø> (+0.18%)	⬆️
src/convergence.jl	0.00% <0.00%> (ø)

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