Add proper documentation to MadNLP

[frapac]

First stab

[sshin23]

Great work, @frapac! I love what you did in solver.md and kkt.md. I'll merge it right away after fixing the URL typo

[sshin23]

url should be github.com/MadNLP/MadNLP.jl.git

[sshin23]

also in line 11

[codecov-commenter]

Codecov Report

Merging #176 (c92758f) into master (5f0a21d) will decrease coverage by 0.19%.
The diff coverage is n/a.

❗ Current head c92758f differs from pull request most recent head 7b67004. Consider uploading reports for the commit 7b67004 to get more accurate results

@@            Coverage Diff             @@
##           master     #176      +/-   ##
==========================================
- Coverage   75.12%   74.93%   -0.20%     
==========================================
  Files          38       38              
  Lines        3405     3351      -54     
==========================================
- Hits         2558     2511      -47     
+ Misses        847      840       -7     

Impacted Files	Coverage Δ
src/KKT/KKTsystem.jl	97.22% <ø> (-0.08%)	⬇️
src/LinearSolvers/linearsolvers.jl	0.00% <ø> (ø)
lib/MadNLPPardiso/src/pardisomkl.jl	90.62% <0.00%> (-3.23%)	⬇️
src/utils.jl	62.50% <0.00%> (-2.21%)	⬇️
src/options.jl	84.61% <0.00%> (-1.10%)	⬇️
src/matrixtools.jl	85.07% <0.00%> (-0.44%)	⬇️
lib/MadNLPMumps/src/MadNLPMumps.jl	82.92% <0.00%> (-0.41%)	⬇️
lib/MadNLPHSL/src/ma57.jl	75.40% <0.00%> (-0.40%)	⬇️
lib/MadNLPHSL/src/ma97.jl	84.00% <0.00%> (-0.32%)	⬇️
lib/MadNLPHSL/src/ma86.jl	84.90% <0.00%> (-0.28%)	⬇️
... and 8 more

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[frapac]

Thanks for the feedback @sshin23 !