Algorithms constructors

[lostella]

This PR refactors the algorithms API, by splitting an algorithm construction (with parameters and so on), and its application to a problem. E.g.:

algorithm = ForwardBackward(parameters...)
x, it = algorithm(f=f, A=A, g=g)

@nantonel: I will prepare a PR to StructuredOptimization.jl so we can check in parallel if this looks OK for that too.

[codecov-io]

Codecov Report

Merging #22 into master will decrease coverage by 4.53%.
The diff coverage is 77.5%.

@@            Coverage Diff            @@
##           master     #22      +/-   ##
=========================================
- Coverage   93.93%   89.4%   -4.54%     
=========================================
  Files          12      12              
  Lines         445     500      +55     
=========================================
+ Hits          418     447      +29     
- Misses         27      53      +26

Impacted Files	Coverage Δ
src/utilities/iterationtools.jl	78.18% <40%> (-21.82%)	⬇️
src/algorithms/primaldual.jl	80.23% <81.81%> (-2.05%)	⬇️
src/algorithms/forwardbackward.jl	92.53% <82.35%> (-4.13%)	⬇️
src/algorithms/douglasrachford.jl	90.9% <84.61%> (-9.1%)	⬇️
src/algorithms/panoc.jl	93.61% <86.66%> (-1.89%)	⬇️
src/algorithms/zerofpr.jl	92.4% <86.66%> (-2.19%)	⬇️
src/algorithms/davisyin.jl	95.12% <88.88%> (-4.88%)	⬇️

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