Introduce "Compiler takes too long" section in Chapter 10 of User's Guide

Currently Chapter 10 ("What to do when something goes wrong") describes two categories of issues: When the compiler “does the wrong thing” and When your program “does the wrong thing”. However, I think the most common "wrong thing" which users encounter is the compiler is taking too long.

Perhaps we should add a section to this chapter providing guidance to users for decreasing their compilation times. This might include:

• Reducing optimisation level
• Auditing codebase for unnecessary INLINE pragmas
• Using cheaper implementations (e.g. Use Enum-based instead of Generic-based serialisation for enumerations)