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>

README.md

@@ -107,6 +107,14 @@ to [Expr Language Definition](https://expr-lang.org/docs/language-definition).
 - name: block google socks
   action: block
   expr: string(socks?.req?.addr) endsWith "google.com" && socks?.req?.port == 80
+
+- name: block bilibili geosite
+  action: block
+  expr: geosite(string(tls?.req?.sni), "bilibili")
+
+- name: block CN geoip
+  action: block
+  expr: geoip(string(ip.dst), "cn")
 ```
 
 #### Supported actions