Expose more information to project.xml users.

[player-03]

Previously, they could access ${app.file} and ${config.android}, but not ${project.platformType} or ${config.android.target-sdk-version}. Now they can!

I don't know if we'd want to phase out ${projectDirectory}, but it's now an option.

[player-03]

Some additions I've considered:

• Access map properties. I've already implemented this, still using the dot access syntax. It's a bit weird considering that isn't how you normally interact with maps.
• Add a parent variable to ProjectXMLParser that points to the project above. Then you can use dot access to get parent.parent.workingDirectory or whatever.
• Make some adjustments so that you can always use the result value in conditionals. For instance, if="${targetFlags.clean}".