Add FFI bindings for libcurl's lifecycle management APIs

[rdw-software]

Separate tracking issue (mostly for testing GitHub's new sub-issues feature...).

Bindings coverage:

• curl_free (should be handled by LuaJIT itself, but it could still be exposed anyway?)
• curl_global_cleanup (handled by the runtime)
• curl_global_init (handled by the runtime)
• curl_global_init_mem (should probably be handled by the runtime as well?)

Some of them probably shouldn't be exported as the environment is managed by the runtime itself.

The individual data types also have their own allocation/deallocation methods. These could be handled with ffi.gc?

[rdw-software]

At least for the initial version, its should be fine to expose curl_free, skip assigning the LuaJIT allocator, and handle the global initialization/cleanup steps in the runtime itself. I don't have a use case for letting scripts do this at hand.

Allocations itself are going to be slower than necessary and that should be fixed in a separate iteration. The problem extends to many more bindings and it doesn't seem extremely important to do this right now. Perf is at best "OK" anyway.