Use macro for implementations of ops traits on references

[tim-blackbird]

• Reduce bloat in the template by using a macro for the reference based ops from Ops propagation #549.
• Makes it easier to add these implementations for other types/ops too :) Implement std::ops traits on references #335

I added a naive snake_case filter to tera to avoid needing to specify the method name at every macro invocation.

The macros itself is.. pretty gross, as expected.

There is only a slight aesthetic change to the generated code. Self to {{ self_t }} for the XXXAssign ops.

[bitshifter]

Wow, you've been busy! I will get around to reviewing all of these sometime this week hopefully

[bitshifter]

One small change request which I think should result in the generated code being the same, or close to the same.