Rewrite of the entrypoint in Golang (#71)

- General improvements
    - Parallel download of only needed files at start
    - Prettier console output with all streams merged (openvpn, unbound, shadowsocks etc.)
    - Simplified Docker final image
    - Faster bootup
- DNS over TLS
    - Finer grain blocking at DNS level: malicious, ads and surveillance
    - Choose your DNS over TLS providers
    - Ability to use multiple DNS over TLS providers for DNS split horizon
    - Environment variables for DNS logging
    - DNS block lists needed are downloaded and built automatically at start, in parallel
- PIA
    - A random region is selected if the REGION parameter is left empty (thanks @rorph for your PR)
    - Routing and iptables adjusted so it can work as a Kubernetes pod sidecar (thanks @rorph for your PR)

internal/settings/shadowsocks.go

@@ -0,0 +1,48 @@
+package settings
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/qdm12/private-internet-access-docker/internal/params"
+)
+
+// ShadowSocks contains settings to configure the Shadowsocks server
+type ShadowSocks struct {
+	Enabled  bool
+	Password string
+	Log      bool
+	Port     uint16
+}
+
+func (s *ShadowSocks) String() string {
+	if !s.Enabled {
+		return "ShadowSocks settings: disabled"
+	}
+	settingsList := []string{
+		"ShadowSocks settings:",
+		fmt.Sprintf("Port: %d", s.Port),
+	}
+	return strings.Join(settingsList, "\n |--")
+}
+
+// GetShadowSocksSettings obtains ShadowSocks settings from environment variables using the params package.
+func GetShadowSocksSettings(params params.ParamsReader) (settings ShadowSocks, err error) {
+	settings.Enabled, err = params.GetShadowSocks()
+	if err != nil || !settings.Enabled {
+		return settings, err
+	}
+	settings.Port, err = params.GetShadowSocksPort()
+	if err != nil {
+		return settings, err
+	}
+	settings.Password, err = params.GetShadowSocksPassword()
+	if err != nil {
+		return settings, err
+	}
+	settings.Log, err = params.GetShadowSocksLog()
+	if err != nil {
+		return settings, err
+	}
+	return settings, nil
+}