Added LRU#maximum=/maximum

This allows one to change the maximum amount of keys stored in the
XPath/CSS caches, for example:

    Oga::XPath::Parser::CACHE.maximum = 2056

lib/oga/lru.rb

@@ -33,6 +33,24 @@ module Oga
       @owner   = Thread.current
     end
 
+    ##
+    # @param [Fixnum] value
+    #
+    def maximum=(value)
+      synchronize do
+        @maximum = value
+
+        resize
+      end
+    end
+
+    ##
+    # @return [Fixnum]
+    #
+    def maximum
+      return synchronize { @maximum }
+    end
+
     ##
     # Returns the value of the key.
     #

spec/oga/lru_spec.rb

@@ -1,6 +1,34 @@
 require 'spec_helper'
 
 describe Oga::LRU do
+  describe '#maximum=' do
+    it 'sets the maximum amount of keys' do
+      cache = described_class.new(10)
+
+      cache.maximum = 20
+
+      cache.maximum.should == 20
+    end
+
+    it 'resizes the cache when needed' do
+      cache = described_class.new(2)
+
+      cache[:a] = 10
+      cache[:b] = 20
+
+      cache.maximum = 1
+
+      cache.size.should == 1
+      cache.keys.should == [:b]
+    end
+  end
+
+  describe '#maximum' do
+    it 'returns the maximum amount of keys' do
+      described_class.new(5).maximum.should == 5
+    end
+  end
+
   describe '#[]' do
     it 'returns nil for a non existing key' do
       described_class.new[:a].should be_nil