[Sync-EN] Add POST examples to the cURL examples chapter

[lacatoire]

Syncs reference/curl/examples.xml with php/doc-en#4612.

• Adds the two new examples: sending a form-encoded POST request and sending a raw JSON POST request, with their code comments translated.
• The chapter section is retitled to the plural form, and the intro paragraph is split so the fetch-homepage example gets its own lead-in.
• The homepage example drops its trailing ?>, as upstream.

EN-Revision bumped to e7c6a2f6847c3a8c9fec6ba588f235ccdcf6f3a5.

Fixes: #1666