C++ support for decimal floating point

[Benjamin Kosnik]

> For the library support I have all of the functionality of section 3.1
> of the TR implemented, with the exception of formatted input and
> output. More importantly, I have a comprehensive set of tests for that
> functionality that will be useful even if the implementation changes.

Oh, and this sounds very encouraging. Thanks for the heads up.

Please don't forget to document what users can expect and or known
limitations. (Trying to be better about documentation all around and
unfortunately new features are the easiest to enforce.)

-benjamin