Simple way to handle rvalues and templates.

[Chris Piker]

Hi D

I have bit of code that was tripping me up.  I need to parse 
small fields out of a big binary read, and it looks like some 
operations just can't be composed when it comes to
using templates.  So this works:
```d
import std.bitmanip, std.system;
ubyte[8192] data;

ubyte[] temp = data[4..6];
ushort us = temp.read!(ushort, Endian.bigEndian);
// intentionally provided the default byte order for readability
```
But this doesn't work:
```d
import std.bitmanip, std.system;
ubyte[8192] data;

ushort us = data[4..6].read!(ushort, Endian.bigEndian);
```
The reasons for this are probably old hat for seasoned D 
programmers by this is really confusing for newbies.

Is there a better way to handle this instead of making a bunch of 
temporary variables that I don't care about?  Matlab has this 
behavior too, statements that should be composable aren't, and it 
drives me crazy since Java and Python don't seem to suffer from 
this problem near a much.