Add pom.xml to enable Maven builds and release management

Hi, so this should hopefully be all ready now.  With the pom.xml in place you can begin to build using maven or continue to use Ant.

Users can add android-query to their maven enabled projects with:

```
<dependency>
    <groupId>com.googlecode.android-query</groupId>
    <artifactId>android-query</artifactId>
    <version>0.24.3</version>
</dependency>
```

I'd recommend you add this info to the googlecode page.

In regards to future releases, if you would be interested in doing them you would need to create a Sonatype JIRA account as outlined at https://docs.sonatype.org/display/Repository/Sonatype+OSS+Maven+Repository+Usage+Guide , and then let me know so I can request your account gets added to the list of users authorised to stage/promote releases.

If you're not too bothered with learning the ins and outs of Maven right now (I wouldn't blame you!), I can continue to help out by pushing up releases whenever they're ready.

Any questions just let me know.

-Paul