Use libtool to build standalone library.
Use libtool to build standalone library.

This makes libusual act like standard lib
and support both shared and static libs.

mgjv/libusual,ifduyue/libusual,mgjv/libusual,mgjv/libusual,markokr/libusual,markokr/libusual,ifduyue/libusual,markokr/libusual,rabbitt/libusual,rabbitt/libusual,markokr/libusual,rabbitt/libusual,ifduyue/libusual,rabbitt/libusual,mgjv/libusual,ifduyue/libusual