refactor dubbo examples & add datasource feature in example & update docs

spring-cloud-alibaba-examples/sentinel-dubbo-api/pom.xml

@@ -0,0 +1,30 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+
+    <parent>
+        <groupId>org.springframework.cloud</groupId>
+        <artifactId>spring-cloud-alibaba-examples</artifactId>
+        <version>0.2.0.BUILD-SNAPSHOT</version>
+    </parent>
+    <modelVersion>4.0.0</modelVersion>
+
+
+    <artifactId>sentinel-dubbo-api</artifactId>
+    <packaging>jar</packaging>
+    <description>api for sentinel dubbo example</description>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-deploy-plugin</artifactId>
+                <version>${maven-deploy-plugin.version}</version>
+                <configuration>
+                    <skip>true</skip>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+
+</project>

spring-cloud-alibaba-examples/sentinel-dubbo-api/src/main/java/org/springframework/cloud/alibaba/cloud/examples/FooService.java

@@ -0,0 +1,10 @@
+package org.springframework.cloud.alibaba.cloud.examples;
+
+/**
+ * @author fangjian
+ */
+public interface FooService {
+
+    String hello(String name);
+
+}