This commit will fix .deb packaging instructions for Ubuntu 16.04.
Meanwhile, .deb packaging for Debian/Ubuntu is now only suitable
for Ubuntu 16.04 LTS or higher, Debian 9 or higher.
Debian 8 users won't be able to build from source too because this
project now requires libsodium >= 1.0.8. Jessie-packports is needed
to build on Debian 8.
Note:
Debian/Ubuntu users may have to `sudo rm -f /etc/shadowsocks` before install
the new `shadowsocks-libev` package.
For library user, the pkg-config package is renamed to `shadowsocks-libev` but
the library name is still the `libshadowsocks` (use `-lshadowsocks` to link)