Add cache system for configs, rulesets and subscriptions

Add proxy_config option for downloading external config files.
Optimize codes.

base/pref-new.yml

@@ -11,6 +11,7 @@ common:
   mellow_rule_base: base/mellow.conf
   quan_rule_base: base/quan.conf
   quanx_rule_base: base/quanx.conf
+  proxy_config: SYSTEM
   proxy_ruleset: SYSTEM
   proxy_subscription: NONE
   append_proxy_type: false
@@ -76,3 +77,7 @@ advanced:
   print_debug_info: false
   max_pending_connections: 10240
   max_concurrent_threads: 4
+  enable_cache: false
+  cache_subscription: 60
+  cache_config: 300
+  cache_ruleset: 21600

base/pref.ini

@@ -36,8 +36,9 @@ quan_rule_base=base/quan.conf
 ;Quantumult X config base used by the generator, supports local files/URL
 quanx_rule_base=base/quanx.conf
 
-;Proxy used to download rulesets or subscriptions, set to NONE or empty to disable it, set to SYSTEM to use system proxy.
+;Proxy used to download configs, rulesets or subscriptions, set to NONE or empty to disable it, set to SYSTEM to use system proxy.
 ;Accept cURL-supported proxies (http:// https:// socks4a:// socks5://)
+proxy_config=SYSTEM
 proxy_ruleset=SYSTEM
 proxy_subscription=NONE
 
@@ -154,3 +155,7 @@ port=25500
 print_debug_info=false
 max_pending_connections=10240
 max_concurrent_threads=4
+enable_cache=false
+cache_subscription=60
+cache_config=300
+cache_ruleset=21600