[EPIC] Optimisation improvements

[jonblack]

Looking at the code there are a lot of improvements that can be made to optimise the code. Profile each case before implementing and check that it indeed improves performance.

Let's chat before implementing anything.

• Don't return copies of objects (alternatives are pointers, references and rvalue references, be careful with the latter. Move semantics take time to get used to.)
• Don't pass by value. Pass by either const reference or pointer (raw or smart) or rvalue reference (move semantics if transferring ownership)