Moved documentation of nua_options(), nua_i_options, nua_i_refer,
nua_message(), nua_i_message, nua_r_message.

Added documentation of nua_i_register, nua_i_outbound.

darcs-hash:20061027132439-65a35-c14ef4d7e99bd5f442da19d3770bd08fb4adf849.gz