#151 SafeFormat review format specification

[Jean-François Bastien]

As detailed in http://accu.org/index.php/journals/1539

It is possible to specify one argument type in the format string and pass in a different type, using positional markers instead of printf-like type specifiers would make this impossible.

Add a policy for this or branch?

See what C# does, especially with respect to width, alignment and special formatting.

This would also allow SafeFormat to support more argument types: we could support exceptions and container types automatically, and allow user defined types (coupled with access shims).