enums and version/static if/"inheritance"

[IchorDev]

I’ve recently made a API for doing this in BindBC-Common. You can 
see it on the latest commit of my repository 
[here](https://github.com/BindBC/bindbc-common/blob/f9b30591e05238fcda80bb6b070acacd1f77f018/source/bindbc/common/codegen.d#L500). This is not tagged as a version yet, but you can download it & use `dub add-local` until I tag it.

It’s designed for making language bindings (mostly to C) so 
there’s a convenient way to have a D version of the enum (e.g. 
`Plant.flower`) and a C version (e.g. `PLANT_FLOWER`) with the 
same code. And you can turn them on and off easily so that people 
who don’t like one of the styles are still happy.
Usage is like…
```d
import bindbc.common;

mixin(makeEnumBindFns(cStyle: true, dStyle: true)); //this 
defines `makeEnumBind`

//makes `enum Plant: ulong`:
mixin(makeEnumBind(q{Plant}, q{ulong}, members: (){
   EnumMember[] ret = [
     {{q{flower}, q{PLANT_FLOWER}}, q{1}},
     {{q{bush},   q{PLANT_BUSH}},   q{2}},
   ];
   if(condition){
     EnumMember[] add = [
       {{q{herb},   q{PLANT_HERB}},   q{4}},
     ];
     ret ~= add;
   }
   return ret;
}()));
```
Please note that some parameters and fields are **required** to 
be referred to by name. Read the documentation comments for 
`makeEnumBind`, `EnumMember`, and `EnumIden` to avoid misusing 
them.