Small improvements and fixes

[jaguililla]

Small improvements and fixes:

• Any media type
• Fix case types regex
• Improve API documentation
• Regroup some utility methods
• Improve settings loading method
• Move basic auth
• Fix HTTP client errors
• Add utility interfaces to extend HTTP handlers
• Fix HTTP handlers context 'receive' method
• Fix REST serialize callbacks
• Improve REST testing tools

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• The PR has a meaningful title.
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• The code pass all PR checks.
• All public members are documented using KDoc.
• The code follow the coding conventions stated at the contributing.md file.