Add support for Index & Range

[Nigel-Ecma]

Alternative to #605

• Add support for Index & Ranges
• Details of types and "implicit support" in new chapter, temporarily at end to reduce lots of changes due to renumbering
• Attempts to avoid all implementation specific details from source material
• Covers dynamic binding, associativity, etc.
• Updates grammar test reference files (adding a new layer to the expression stack changes the tree but not the parse). These files can be ignored for review (they are machine generated).
• Adds a new grammar test with Index & Range samples