Add GeoIP and GeoSite support for expr (#38)

* feat: copy something from hysteria/extras/outbounds/acl

* feat: add geoip and geosite support for expr

* refactor: geo matcher

* fix: typo

* refactor: geo matcher

* feat: expose config options to specify local geoip/geosite db files

* refactor: engine.Config should not contains geo

* feat: make geosite and geoip lazy downloaded

* chore: minor code improvement

* docs: add geoip/geosite usage

---------

Co-authored-by: Toby <tobyxdd@gmail.com>

ruleset/builtins/geo/interface.go

@@ -0,0 +1,27 @@
+package geo
+
+import (
+	"fmt"
+	"net"
+
+	"github.com/apernet/OpenGFW/ruleset/builtins/geo/v2geo"
+)
+
+type HostInfo struct {
+	Name string
+	IPv4 net.IP
+	IPv6 net.IP
+}
+
+func (h HostInfo) String() string {
+	return fmt.Sprintf("%s|%s|%s", h.Name, h.IPv4, h.IPv6)
+}
+
+type GeoLoader interface {
+	LoadGeoIP() (map[string]*v2geo.GeoIP, error)
+	LoadGeoSite() (map[string]*v2geo.GeoSite, error)
+}
+
+type hostMatcher interface {
+	Match(HostInfo) bool
+}