[phobos] tie for std.typecons.Tuple

[Masahiro Nakagawa]

Hi,

Currently, Phobos has Tuple but doesn't have tie.
So I implemented tie for std.typecons.Tuple.

http://www.bitbucket.org/repeatedly/scrap/src/tip/tie_.d

Original author is 9rnsr but his version is a bit messy and overkill.
I substantially rewrote his tie.
- clear syntax (tie(&n, &d) => tie(n, d))
- Implicit conversion

I would like to suggest this tie is integrated into phobos.

What do you think of this?