use emplaceRef in join

And remove old trustedAllocateArray.
uninitializedArray is already trusted.
Include NullSink in std.range ddocs.

Partial fix for makefile to build std.range docs, that was broken after
std.range was split. This is only a partial fix; the full fix will have
to be done as part of [issue 13766] (https://issues.dlang.org/show_bug.cgi?id=13766).
Merge pull request #2763 from quickfur/nullsink_ddoc

Include NullSink in std.range ddocs.
Merge pull request #2747 from 9il/join2

use emplaceRef in join