Add FFI bindings for libcurl's "easy" interface

[rdw-software]

Bindings coverage:

• curl_easy_cleanup
• curl_easy_duphandle
• curl_easy_escape
• curl_easy_getinfo
• curl_easy_header
• curl_easy_init
• curl_easy_nextheader
• curl_easy_option_by_id
• curl_easy_option_by_name
• curl_easy_option_next
• curl_easy_pause
• curl_easy_perform
• curl_easy_recv
• curl_easy_reset
• curl_easy_send
• curl_easy_setopt
• curl_easy_ssls_import
• curl_easy_ssls_export
• curl_easy_strerror
• curl_easy_unescape
• curl_easy_upkeep

See https://curl.se/libcurl/c/libcurl-easy.html

[rdw-software]

I'd be interested to see how usable this actually is (while blocking the event loop). Obviously not great do do that when you can use coroutines or some other mechanism, but until the async APIs are streamlined it's better than nothing.