add version setter / getter

In this commit, user can set / get api version client uses.

```java
AmazonRoute53Client client = new AmazonRoute53Client();
client.set("2013-12-12");
```

above code changes hardcoded paths:

```
String uriResourcePath = "/2012-12-12/hostedzone"; 
```

to dynamically version dependent paths.

```
String uriResourcePath = "/{Version}/hostedzone";
uriResourcePath = uriResourcePath.replace("{Version}", version);
```