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/settings.go

@@ -0,0 +1,60 @@
+package settings
+
+import (
+	"strings"
+
+	"github.com/qdm12/private-internet-access-docker/internal/params"
+)
+
+// Settings contains all settings for the program to run
+type Settings struct {
+	OpenVPN     OpenVPN
+	PIA         PIA
+	DNS         DNS
+	Firewall    Firewall
+	TinyProxy   TinyProxy
+	ShadowSocks ShadowSocks
+}
+
+func (s *Settings) String() string {
+	return strings.Join([]string{
+		"Settings summary below:",
+		s.OpenVPN.String(),
+		s.PIA.String(),
+		s.DNS.String(),
+		s.Firewall.String(),
+		s.TinyProxy.String(),
+		s.ShadowSocks.String(),
+		"", // new line at the end
+	}, "\n")
+}
+
+// GetAllSettings obtains all settings for the program and returns an error as soon
+// as an error is encountered reading them.
+func GetAllSettings(params params.ParamsReader) (settings Settings, err error) {
+	settings.OpenVPN, err = GetOpenVPNSettings(params)
+	if err != nil {
+		return settings, err
+	}
+	settings.PIA, err = GetPIASettings(params)
+	if err != nil {
+		return settings, err
+	}
+	settings.DNS, err = GetDNSSettings(params)
+	if err != nil {
+		return settings, err
+	}
+	settings.Firewall, err = GetFirewallSettings(params)
+	if err != nil {
+		return settings, err
+	}
+	settings.TinyProxy, err = GetTinyProxySettings(params)
+	if err != nil {
+		return settings, err
+	}
+	settings.ShadowSocks, err = GetShadowSocksSettings(params)
+	if err != nil {
+		return settings, err
+	}
+	return settings, nil
+}