Renaming std.conv

[Sean Kelly]

Andrei Alexandrescu Wrote:
>
> We haven't reached consensus on where to put enforce() and friends. Any 
> other ideas? Of the above, I like std.checks.
> 
> Better yet, how about defining std.exception that includes a host of 
> exception-related functionality (such as defining exceptions that retain 
> file and line, perhaps stack traces etc.)?

The trace functionality already exists in druntime.  As for exceptions, they may belong there as well if they're ones the runtime should be aware of.