Added CSS/XPath Parser.parse_with_cache

This method parses and caches ASTs using Oga::LRU. Currently the default
of 1024 keys is used.

See #71 for more information.

lib/oga/css/parser.rll

@@ -310,6 +310,19 @@ even
 
 %inner
 {
+  ##
+  # @return [Oga::LRU]
+  #
+  CACHE = LRU.new
+
+  ##
+  # @param [String] data
+  # @return [AST::Node]
+  #
+  def self.parse_with_cache(data)
+    return CACHE.get_or_set(data) { new(data).parse }
+  end
+
   ##
   # @param [String] data The input to parse.
   #

lib/oga/xpath/parser.rll

@@ -223,6 +223,19 @@ variable
 
 %inner
 {
+  ##
+  # @return [Oga::LRU]
+  #
+  CACHE = LRU.new
+
+  ##
+  # @param [String] data
+  # @return [AST::Node]
+  #
+  def self.parse_with_cache(data)
+    return CACHE.get_or_set(data) { new(data).parse }
+  end
+
   ##
   # @param [String] data The input to parse.
   #