Transitions to new language semantics

[singingbush]

There have been so many breaking changes in D that I've kept a 
few useful version checks in this gist: 
https://gist.github.com/SingingBush/3a2a6d2a41a81c1bafb26e5f69f823c0

for things like

```
     static if (__VERSION__ < 2074) {
         import std.traits : FieldTypeTuple, Filter; // Filter 
used to be in std.traits
     } else {
         import std.traits : FieldTypeTuple;
         import std.meta : Filter;
     }
```

and

```
     // JSON_TYPE is now JSONType simply due to code style: 
https://issues.dlang.org/show_bug.cgi?id=19135
     static if(__VERSION__ >= 2082)
         import std.json : JSONType;
     else
         alias JSONType = std.json.JSON_TYPE;
```

this is one of my main problems with using D. There are breaking 
changes far to often. Generally with little to no overlap 
allowing time for developers to update code.

With GDC only supporting D 2.076 and the latest D release being 
2.097 there's a whole range of D versions that dub packages 
should support if they are to work across all compilers. Sadly 
though, very few will work with a range of D versions that wide.

While ever this statement remains true; "D code written with 
latest dmd today may not compile with latest dmd in 12 months 
time", then D cannot really be considered for use by most 
organisations. This is the biggest problem with the D ecosystem