debian: Update packaging instructions (Fix #1198)

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.

debian/README.Debian

@@ -1,15 +1,11 @@
 shadowsocks-libev for Debian
-----------------------
+----------------------------
 
 The Debian package has added systemd support. A default server service which
 reads the default configuration in /etc/default/shadowsocks-libev is installed
 and enabled by default, plus some other service templates placed in
 /lib/systemd/system, which can be used by users later.
 
-Another problem is that shadowsocks-libev is licensed under GPLv3+. This will
-conflict with OpenSSL License when linked against OpenSSL library. As a
-result, this package faces licensing problem. Use it at your own risk.
-
  -- Boyuan Yang <073plan@gmail.com>  Wed, 14 Oct 2015 09:18:50 +0800
 
 (No special notes.)

debian/control

@@ -7,12 +7,16 @@ Build-Depends:
  autotools-dev,
  debhelper (>= 9),
  dh-systemd (>= 1.5),
+ dh-autoreconf,
  gawk,
  libpcre3-dev,
- libssl-dev (>= 0.9.8),
+ libmbedtls-dev,
+ libsodium-dev (>= 1.0.8~),
+ libudns-dev,
+ libev-dev,
  mime-support,
  pkg-config,
- xmlto
+ xmlto,
 Standards-Version: 3.9.8
 Homepage: https://www.shadowsocks.org
 Vcs-Git: https://github.com/shadowsocks/shadowsocks-libev.git

debian/rules

@@ -25,4 +25,4 @@ override_dh_shlibdeps:
 	dh_shlibdeps --dpkg-shlibdeps-params=--ignore-missing-info
 
 %:
-	dh $@ --with systemd
+	dh $@ --with systemd,autoreconf