Just another example of missing string interpolation

[Richard (Rikki) Andrew Cattermole]

I decided to have a go and do my own little proposal. Its a pretty big 
mesh of things, with one key difference, the notion of a binary-less 
expression. This simplifies the grammar quite a bit and should do the 
same for the implementation.

https://gist.github.com/rikkimax/90a4b21feabcf34dbecb8efcb587f8e1

```d
stderr.write("$clear\r${white}Progress:$clear$progress% 
\t${white}Speed:$clear $curSpeed $unit");
```

It should be familiar to both C++ and Python folk.

I've already implemented a formatter read/write for ``{:}`` syntax so I 
might be a tad biased, especially since I want to use ``$Identifier`` 
for something (not that it conflicts here).