shadowsocks-libev: rewrite

- Selecting only a single or subset of all components of shadowsocks-libev is
  now possible (this is the main motivation behind the rewrite)
- Configuring multiple instances of the same component is now also possible
- Same option names as with the json config
- Unified configuration generation method for each component
- Add support for ss-local, ss-tunnel, ss-server
- Most data validation is now done with validate_data
- USE_PROCD=1
- Update ss-rules with the one from shadowsocks/luci-app-shadowsocks
- Add README.md
- Set myself as the maintainer

Addresses #4435

Signed-off-by: Yousong Zhou <yszhou4tech@gmail.com>

net/shadowsocks-libev/files/ss-rules.defaults

@@ -0,0 +1,10 @@
+#!/bin/sh
+
+s=firewall.ss_rules
+uci get "$s" >/dev/null && exit 0
+uci batch <<-EOF
+	set $s=include
+	set $s.path=/etc/firewall.ss-rules
+	set $s.reload=1
+	commit firewall
+EOF