We should deprecate -release

[Steven Schveighoffer]

The `-release` flag is equivalent to `-O -boundscheck=safeonly 
-inline`.

I think we should remove it. If you want no bounds checks, you 
should have to really want it enough to type that whole 
monstrosity in. It's trivial to avoid bounds checks by using 
`.ptr[index]` in `@system` code. In my dub projects, I rewrite 
the release mode to keep bounds checks for all code, it's that 
important.

What do you think? Deprecate for 3 versions, then remove.

-Steve