!238 添加Column类型接口

Merge pull request !238 from mcck/N/A

mybatis-plus-core/src/main/java/com/baomidou/mybatisplus/core/conditions/segments/ColumnSegment.java

@@ -0,0 +1,7 @@
+package com.baomidou.mybatisplus.core.conditions.segments;
+
+import com.baomidou.mybatisplus.core.conditions.ISqlSegment;
+
+@FunctionalInterface
+public interface ColumnSegment extends ISqlSegment {
+}