DIP54 : revamp of Phobos tuple types

[Dicebot]

Have updated the DIP to include feedback from this thread : 
http://wiki.dlang.org/DIP54

It effectively means resorting back to both std.meta.pack and 
std.meta.list as a compromise.

Unfortunately I was not able to hack compiler into doing opSlice 
overloading desired for hygienic TemplateArgumentPack 
implementation. opSlice itself is doable but I have a big problem 
with existing opDollar implementation which effectively replaces 
$ with a reference to local variable __dollar__ making it 
impossible to use one in contexts where no hidden variable can be 
injected. Restructuring frontend to use different opDollar 
semantics is beyond my current knowledge and I want to move 
forward with it.

Hope to start working on it soon. Ironically, getting a D job has 
stripped me of almost all time spent on side D tasks so progress 
is very slow, sorry :(