add current_page and back

spec/agent_spec.cr

@@ -91,4 +91,13 @@ describe "Mechanize Agent test" do
     agent.history.size.should eq 2
     agent.history.last.title.should eq "page_title"
   end
+
+  it "can back previous page" do
+    agent = Mechanize.new
+    agent.get("http://example.com/")
+    agent.get("http://html_example.com/")
+    agent.current_page.title.should eq "page_title"
+    agent.back
+    agent.current_page.title.should eq ""
+  end
 end

src/mechanize.cr

@@ -60,6 +60,14 @@ class Mechanize
     @agent.request_headers = request_headers
   end
 
+  def current_page
+    @agent.current_page
+  end
+
+  def back
+    @agent.history.pop
+  end
+
   def submit(form)
     case form.method.upcase
     when "POST"

src/mechanize/http/agent.cr

@@ -37,6 +37,10 @@ module MechanizeCr
         end
       end
 
+      def current_page
+        @history.last
+      end
+
       def back
         @history.pop
       end
@@ -102,10 +106,6 @@ module MechanizeCr
         end
       end
 
-      private def current_page
-        @history.last
-      end
-
       private def reset_request_header_cookies
         request_headers.delete("Cookie")
       end