v2: Expose Original Format-Specific Feed Data

[mmcdole]

Overview

Add support for preserving and exposing the original format-specific parsed feed object (atom.Feed, rss.Feed, or json.Feed) in the universal gofeed.Feed structure.

Tasks

• [ ] Add OriginalFeed interface{} field to gofeed.Feed struct
• [ ] Update translators to populate OriginalFeed when ParseOptions.KeepOriginalFeed is true
• [ ] Add helper methods or type assertions guidance for accessing format-specific data
• [ ] Document how to access RSS-specific fields like skipHours, skipDays, etc.
• [ ] Add tests for OriginalFeed preservation across all feed formats

Benefits

• Access to format-specific fields not mapped to universal model
• Ability to retrieve RSS "source" attributes (#229, #235)
• Access to RSS scheduling hints like skipHours (#228)
• Preserves all original data while maintaining universal interface

Related Issues

• #229 (RSS source attribute)
• #235 (Exposing original feed)
• #228 (RSS skipHours)

Parent Issue

• #241 (RFC: gofeed v2)

[mmcdole]

This has been implemented in PR #258. The OriginalFeed field is now available when KeepOriginalFeed is set to true in ParseOptions.