Can std.conv.toImpl please be deprecated

[Jack Stouffer via Digitalmars-d]

Before I opened a PR, I wanted to get some second opinions.

There is no reason IMO that the various overloads of toImpl 
should be public. Having the internal functionality of a parent 
function, in this case to, be exposed like this causes:

1. The docs to be cluttered with useless info. Anything pertinent 
can be moved to the to docs.
2. The function cannot be refactored because its guts are shown 
to the world

Also, there is no reason that anyone should use toImpl over to. 
So can I please mark toImpl as deprecated in order to clean up 
std.conv?