Create Library JAR

Addressed issue #1

To create a library jar just update the `version.num` and `sdk.dir` properties in the `build.xml`.

<b>Example:</b>
`<property name="version.num" value="12.08" />`
`<property name="sdk.dir" value="/usr/local/android-sdk/platforms/android-16/" />`

The jar only includes the minimum necessary files for other developers to use the sdk.
I suggest you create a .jar for the current version and insert in the Downloads folder.