Fix `Create Shapes` examples for deprecated `autoglobal`.

 - Fix `Create Shapes` examples for deprecated `autoglobal`.
 - Remove extra spaces at EOL/EOF.
 - Use meaningful identifiers instead of single characters (except in some obvious cases, e.g. `x`, `y`).
 - Use list comprehensions where possible, and where they are not more complicated than the equivalent `for` construct.
 - Refactor `ParticleSystemPShape` considerably.