link::marshalled_options_t and link::option_t should be in namespace detail_

[eyalroz]

Library users never actually need to know about JIToption's (and link::marshalled_options_t), nor about the CUjit_option - since they have our nice and convenient link::options_t class, which they can populate and pass around. Their only real use is internal, and thus - they shoud be placed in the detail_ namespace.