Add a flag to dump generated specialisations

Motivation

It's difficult to tell what specialisations are generated without looking at the Core of a module.

Proposal

Add a -ddump-speciali{s,z}ations flag to dump information about all specialised functions that get generated. I think the most useful information to dump is the identifiers and types of the unspecialised function and the generated specialisation. Specialisations generated from pragmas should also be dumped.