Improve documentation of std.string.column.
Update std.stdio.writef docs.

The docs are outdated; the `writef(stderr, fmt, ...)` syntax is no longer
supported. Also, remove a bunch of really old notes about changes in version
2.006, which are already ancient history. Refer instead to the docs of
std.format.formattedWrite, which are the most up-to-date and accurate docs on
this subject.
Split DList Node into DNode and PayNode.
Merge pull request #2535 from quickfur/issue10164

Improve documentation of std.string.column.
Merge pull request #2540 from quickfur/issue10139

Update std.stdio.writef docs.
Tweak #2532
Merge pull request #2545 from JakobOvrum/issue13467

Tweak #2532
Fix indent
Fix wrong "Orphaned format specifier" error message.

Print out the specifier, not the entire format string!
Make byCodeUnit bidirectional range
Merge pull request #2546 from sinkuu/bycodeunit_bidi

Make byCodeUnit bidirectional range
Merge pull request #2457 from monarchdodra/DNode

Split DList Node into DNode and PayNode.
Merge pull request #2538 from quickfur/issue11539

Fix wrong "Orphaned format specifier" error message.
fix to!string test
Merge pull request #2549 from IgorStepanov/std-conv-unittest

[trivial] [newaa] fix to!string(aa) test