Document const bindings

[poletti-marco]

In some use cases of bindInstance, people might want to bind constants. To support this use case, the following changes are needed:

• Change the normalization of const C, const C& and const C* to be const C (instead of C)
• Forbid binding both const C and C (with tests)
• When a const C binding is required, a C binding can satisfy this requirement (also add tests for this)
• Add tests for bindInstance(const C&)
• Document the caveat of bindInstance(const C&) (the reference must outlive the injector) and add a deleted bindInstance(C&&) overload to make sure temporaries are rejected.
• Update comments and wiki to mention the new kind of binding, add examples to the reference documentation