fix Issue 10230 - Duplicated buttons for runnable examples
Implement toString that supports %f.
Add deprecation date.

Improve documentation for new toString.
Add unittest for issue 6381.

To prevent regressions.
Add TODO to make toString() pure @safe nothrow

I tried each of those qualifiers but none of them compiled due to the
way std.format works right now. So leave it for the future.
Merge pull request #1531 from quickfur/issue6381

Add unittest for issue 6381 (std.math.floor/ceil should be pure)
Merge pull request #1516 from quickfur/complex_format

Fix issue 10881: support writefln("%f") of complex numbers
Merge pull request #1328 from 9rnsr/fix10230

Issue 10230 - Duplicated buttons for runnable examples