Added custom format page to translation component
Link from introduction section
Small fixes
Cleanups
Improvements based on comments
Extra improvements based on comments
Fixed wrong indentation
Improved custom formats article based on comments
feature #4166 Translation custom loaders (raulfraile)

This PR was merged into the 2.3 branch.

Discussion
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Translation custom loaders

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?     | yes
| Applies to    | all
| Fixed tickets | #4156

This PR adds a documentation section for creating custom loaders and dumpers to support other formats.

Commits
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69491ae Improved custom formats article based on comments
c0f3b0a Fixed wrong indentation
629a008 Extra improvements based on comments
bfd78b3 Improvements based on comments
105a168 Cleanups
e2fd5fa Small fixes
dee7fb2 Link from introduction section
8b6c584 Added custom format page to translation component