version(number) is completely useless

[Hipreme]

version(number) actually contains something really nice on it. 
But it is useless.

For example: version(3) would actually declare version(2) and 
version(1).

The problem is that these doesn't mean anything at all, but they 
have this property of waterfall. Which is totally missing in D 
right now. Take this as an example:

```d

version(V1_3)
     version = V1_2;
version(V1_2)
     version = V1_1;
version(V1_1)
     version = V1_0;
```

I need to do this. **per file**. This is such a boilerplate code 
that could get a lot nicer if we had some kind of versioning 
syntax. For example `version(V.1.3)`. We could even get:
`version(SDL.2.5)`. Which would declare everything down to SDL.2.0


Obviously this feature is meaningless to small projects