fix: [doc] follw re-organization (move and rename) of backends

[ssato]

• fix: follow re-organization (re-structure; add, move and rename) of the docs for backend parser modules
• enhancement: add descriptions show how to arrange test data and code for loaders and dumper

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (b57f680) 95.87% compared to head (6f1af2a) 95.87%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## next #160 +/- ## ======================================= Coverage 95.87% 95.87% ======================================= Files 271 271 Lines 4630 4630 ======================================= Hits 4439 4439 Misses 191 191 ```

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