Refactor router for readability

[aldas]

• renamed variables for readability
• refactored tests to table driver (this way it is easier to test each case with breakpoints)

2 commits to separate these changes in history

NB: I took several tests from my own implementation and some of them have FIXME notes. These are to document behaviors where I think currently we are not routing correctly.

For tests to highlight problematic param route + ending with slash - I will provide fix in separate PR as it is quite easy to fix.

[codecov]

Codecov Report

Merging #1796 (eecd0e4) into master (6f9b71c) will increase coverage by 0.03%.
The diff coverage is 99.21%.

@@            Coverage Diff             @@
##           master    #1796      +/-   ##
==========================================
+ Coverage   89.56%   89.60%   +0.03%     
==========================================
  Files          32       32              
  Lines        2646     2656      +10     
==========================================
+ Hits         2370     2380      +10     
  Misses        178      178              
  Partials       98       98              

Impacted Files	Coverage Δ
router.go	96.04% <99.21%> (+0.16%)	⬆️

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[lammel]

Finally readable router code. Awesome.

[lammel]

Great to see comments with diagrams to help understand the testcase.
Hopefully we won't have to change them anytime soon.