Extensive refresh of site for standardized structure

[MikeAdamsMews]

Summary

Extensive refresh of site for a neater, better structured design that is standardized and unified with Connector API and POS API. A number of improvements to wording and presentation were made at the same time. Pathnames to API operations have not changed, but a number of other pathnames have changed. All internal links have been updated, and a .gitbook.yaml redirect file is included as a fallback to redirect any external deep links to old paths. [file to be added]

1. Guidelines changed to Usage guidelines
2. Simplified Usage guidelines home page to follow standard format, and moved content to sub-pages
3. Added new page Authentication
4. Added new page Environments (content moved here from mews-operations/README.md and channel-manager-operations/README.md)
5. Renamed Whitelisting to Allowlisting and moved this content to the Environments page
6. Added new page Compliance
7. Added new section Use cases
8. Added new use case page for Channels (content moved here from old Guidelines page)
9. Added new use case page for Inventory updates (content moved here from old API Operations (CHM) page)
10. API Operations (Mews) promoted to replace mews-operations/README.md and old file mews-operations/operations.md removed; all child pages also promoted
11. API Operations (CHM) promoted to replace channel-manager-operations/README.md and old file channel-manager-operations/operations.md removed; all child pages also promoted
12. Minor improvements to wording, style and presentation throughout.

Checklist

• Documentation follows the Style Guide
• JSON examples updated
• Properties in JSON examples in same order as in property tables
• Changelog dated the day when PR merged
• Changelog accurately describes all changes
• Changelog highlights the affected endpoints or operations
• Changelog highlights any deprecations
• All hyperlinks tested
• Deprecation Table updated if any deprecations
• SUMMARY.md updated if new pages added