Well, regarding Lua 5.2 compatibility, I'm blocked by LuaSec. I could not found any version for 5.2. LuaSocket is almost there, and LuaCrypto... I found there is a pull request waiting to be merged, adding support for it.
On the issue of multipart posts, I adapted some code from lua-multipart. Thanks a lot, Pierre.
Need some time to correct the docs, though.
Regards,
Ignacio