Add lcurl.a target to makefile.
Add lcurl.a target to makefile.

This allows you to build a version of Lua-cURL which can be statically
linked into other programs, making distribution much easier.

moteus/lua-lcurl,moteus/lua-lcurl,Lua-cURL/Lua-cURLv3,Lua-cURL/Lua-cURLv3,Lua-cURL/Lua-cURLv3