New PIA servers support (#227)

* Adapt storage: SyncServers write to file option, export FlushToFile
* CLI built-in updater for old and new PIA servers
* Update hardcoded IP addresses for PIA old and new servers
* Add PIA old to allServers struct and update timestamps
* Adapt code to work with new and old PIA servers
* Remove PIA subdomains (unneeded) from resolver tool

internal/updater/openvpn.go

@@ -0,0 +1,28 @@
+package updater
+
+import (
+	"net"
+	"strings"
+)
+
+func extractRemoteLinesFromOpenvpn(content []byte) (remoteLines []string) {
+	lines := strings.Split(string(content), "\n")
+	for _, line := range lines {
+		if strings.HasPrefix(line, "remote ") {
+			remoteLines = append(remoteLines, line)
+		}
+	}
+	return remoteLines
+}
+
+func extractIPsFromRemoteLines(remoteLines []string) (ips []net.IP) {
+	for _, remoteLine := range remoteLines {
+		fields := strings.Fields(remoteLine)
+		ip := net.ParseIP(fields[1])
+		if ip == nil { // not an IP address
+			continue
+		}
+		ips = append(ips, ip)
+	}
+	return ips
+}