创建 source 包，将 IStringSource 挪到此包中，为后续重构做准备

src/main/java/com/jfinal/template/Engine.java

@@ -22,6 +22,7 @@ import java.util.Map;
 import com.jfinal.kit.HashKit;
 import com.jfinal.kit.StrKit;
 import com.jfinal.template.expr.ast.MethodKit;
+import com.jfinal.template.source.IStringSource;
 import com.jfinal.template.stat.Parser;
 import com.jfinal.template.stat.ast.Stat;
 

src/main/java/com/jfinal/template/EngineConfig.java

@@ -27,6 +27,7 @@ import com.jfinal.template.expr.ast.ExprList;
 import com.jfinal.template.expr.ast.SharedMethodKit;
 import com.jfinal.template.ext.directive.*;
 import com.jfinal.template.ext.sharedmethod.Json;
+import com.jfinal.template.source.IStringSource;
 import com.jfinal.template.stat.Location;
 import com.jfinal.template.stat.Parser;
 import com.jfinal.template.stat.ast.Define;

src/main/java/com/jfinal/template/Env.java

@@ -20,6 +20,8 @@ import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+
+import com.jfinal.template.source.IStringSource;
 import com.jfinal.template.stat.Location;
 import com.jfinal.template.stat.ParseException;
 import com.jfinal.template.stat.ast.Define;

src/main/java/com/jfinal/template/FileStringSource.java

@@ -22,6 +22,8 @@ import java.io.FileInputStream;
 import java.io.IOException;
 import java.io.InputStreamReader;
 
+import com.jfinal.template.source.IStringSource;
+
 /**
  * FileStringSource
  */

src/main/java/com/jfinal/template/MemoryStringSource.java

@@ -18,6 +18,7 @@ package com.jfinal.template;
 
 import com.jfinal.kit.HashKit;
 import com.jfinal.kit.StrKit;
+import com.jfinal.template.source.IStringSource;
 
 /**
  * MemoryStringSource

src/main/java/com/jfinal/template/ext/directive/RenderDirective.java

@@ -23,10 +23,10 @@ import com.jfinal.template.Directive;
 import com.jfinal.template.EngineConfig;
 import com.jfinal.template.Env;
 import com.jfinal.template.FileStringSource;
-import com.jfinal.template.IStringSource;
 import com.jfinal.template.TemplateException;
 import com.jfinal.template.expr.ast.Assign;
 import com.jfinal.template.expr.ast.ExprList;
+import com.jfinal.template.source.IStringSource;
 import com.jfinal.template.stat.Ctrl;
 import com.jfinal.template.stat.ParseException;
 import com.jfinal.template.stat.Parser;

src/main/java/com/jfinal/template/IStringSource.java

@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-package com.jfinal.template;
+package com.jfinal.template.source;
 
 /**
  * IStringSource