Fix type tuple

Fixes `TypeTuple` part of [Issue 4113](http://d.puremagic.com/issues/show_bug.cgi?id=4113).

Still not sure about properly names (except for `expressionTuple` which is titled [in Tuples article](http://dlang.org/tuple.html))

##### Note:
View first commit diff to see `std/{typetuple.d → generictuple.d}` renaming+changes.

[EDITED]
As it shown in the second commit  `TypeTuple` is used ~70% of generic tuple usage.