Update api-endpoints.md

Removing commented out endpoints following confirmation that they're not required.
Update assessment.md

Updates `assignedTo` and `assignedExpiration` information.
Update assessment.md

Adds that retrieved applications are sorted on created date.
Update README.md

Updates with migration info and link to new docs.
Update README.md

Adds revoke webhook.
Merge branch 'master' into doc-tidy
Update webhooks.md
Update assessment.md

Adds pagination info.
Update badges.md

Adds pagination info.
Update claim-codes.md

Adds pagination info.
Update issuers.md

Adds pagination info.
Update issuing.md

Adds pagination info.
Update milestones.md

Adds pagination info.
Update programs.md

Adds pagination info.
Update systems.md

Adds pagination info.
Update milestones.md

Updates milestones auto-awarding info.
Update milestones.md

Adds routes for adding and removing badges from milestones.
Update milestones.md
Update assessment.md

Expands pagination info.
Update badges.md

Expands pagination info.