Pull request: * all: move internal Go packages to internal/

Merge in DNS/adguard-home from 2234-move-to-internal to master

Squashed commit of the following:

commit d26a288cabeac86f9483fab307677b1027c78524
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Fri Oct 30 12:44:18 2020 +0300

    * all: move internal Go packages to internal/

    Closes #2234.

internal/dhcpd/v46_windows.go

@@ -0,0 +1,47 @@
+package dhcpd
+
+// 'u-root/u-root' package, a dependency of 'insomniacslk/dhcp' package, doesn't build on Windows
+
+import "net"
+
+type winServer struct {
+}
+
+func (s *winServer) ResetLeases(leases []*Lease) {
+}
+func (s *winServer) GetLeases(flags int) []Lease {
+	return nil
+}
+func (s *winServer) GetLeasesRef() []*Lease {
+	return nil
+}
+func (s *winServer) AddStaticLease(lease Lease) error {
+	return nil
+}
+func (s *winServer) RemoveStaticLease(l Lease) error {
+	return nil
+}
+func (s *winServer) FindMACbyIP(ip net.IP) net.HardwareAddr {
+	return nil
+}
+
+func (s *winServer) WriteDiskConfig4(c *V4ServerConf) {
+}
+func (s *winServer) WriteDiskConfig6(c *V6ServerConf) {
+}
+
+func (s *winServer) Start() error {
+	return nil
+}
+func (s *winServer) Stop() {
+}
+func (s *winServer) Reset() {
+}
+
+func v4Create(conf V4ServerConf) (DHCPServer, error) {
+	return &winServer{}, nil
+}
+
+func v6Create(conf V6ServerConf) (DHCPServer, error) {
+	return &winServer{}, nil
+}