Add simple InitialStatic alpha choice by providing just a number to t…

[pkofod]

…he alphaguess keyword in method constructors.

Fixes #805

[codecov]

Codecov Report

Merging #812 into master will increase coverage by 0.01%.
The diff coverage is 90.00%.

@@            Coverage Diff             @@
##           master     #812      +/-   ##
==========================================
+ Coverage   81.36%   81.37%   +0.01%     
==========================================
  Files          43       43              
  Lines        2452     2454       +2     
==========================================
+ Hits         1995     1997       +2     
  Misses        457      457              

Impacted Files	Coverage Δ
src/multivariate/solvers/first_order/cg.jl	97.29% <ø> (ø)
src/utilities/perform_linesearch.jl	62.96% <50.00%> (-1.04%)	⬇️
...olvers/first_order/accelerated_gradient_descent.jl	95.65% <100.00%> (ø)
src/multivariate/solvers/first_order/bfgs.jl	100.00% <100.00%> (ø)
...ltivariate/solvers/first_order/gradient_descent.jl	100.00% <100.00%> (ø)
src/multivariate/solvers/first_order/l_bfgs.jl	98.38% <100.00%> (ø)
...e/solvers/first_order/momentum_gradient_descent.jl	94.73% <100.00%> (ø)
src/multivariate/solvers/first_order/ngmres.jl	93.98% <100.00%> (ø)
src/multivariate/solvers/second_order/newton.jl	100.00% <100.00%> (ø)
src/multivariate/solvers/constrained/samin.jl	76.64% <0.00%> (+0.72%)	⬆️

---

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 990c1b3...f7bef75. Read the comment docs.

[CarloLucibello]

thanks for fixing this. Maybe this should be documented somewhere

[pkofod]

Certainly. Where would be a good place to put it? In the method docstrings? Maybe an early mention in the Optim docs as well.