Update Terminology from List to Array

[DavePearce]

The terminology in Whiley is set to change. The "list" type is to be replaced with the "array" type. Hence, all documents need to be updated in two ways:

1. Should refer to array types and array expressions.
2. Should use array type syntax, rather than old list syntax.

[DavePearce]

Ok, have applied (1) and (2) to the document, but the examples are not updated yet. These need to be done when the compiler is ready to type check them.