Update information in SpEL Evaluation chapter in reference manual

[sbrannen]

The SpEL Evaluation chapter in the reference manual contains the following outdated information.

• SimpleEvaluationContext no longer has a create() method. Instead it has forPropertyAccessors(), forReadOnlyDataBinding(), and forReadWriteDataBinding() factory methods.
• SpEL actually cannot automatically create missing array elements or grow the size of an array like it can for a Collection.