Added an example that replicates the Base template

No one should want to do this, but it's the only example I have at the moment.
README tweaks
Added Template#install

Installs a Template into the user's template directory
Install Mac-only templates in the special place
Added ancestor and concrete to ProjectBuilder
Use method_missing in ProjectBuilder
Added platform commands to ProjectBuilder
Added template locations to the readme
Output empty hashes as empty dictionaries because Xcode 5.0.2 will crash if Configurations is empty

An empty ‘Release’ configuration is generated if no configurations have been set
Added support for popup options to the DSL

Very rudimentary, and very sloppy
Added the target_type attribute to Target
Updated the DSL to create a file with content
Switched to custom plist generation

REXML doesn't handle CDATA properly
Renamed to_hash to to_h
Added support for project settings in popup items
Added support for legacy target tool path and arguments