sprintf.NET

For many reasons, a .NET developer should use composite formatting. (Culture-specific, no P/Invoke cost, string interpolation, etc) However, sometimes it is desirable to have a C-style format string, as when sharing localization strings across platforms.

P/Invoke to swprintf is generally sufficient, but:

1. It does not handle params correctly. (Values remain boxed as object and the format becomes the pointer value)
2. Because swprintf is disallowed for Windows Store apps, we must call the strsafe methods.

Thus, we use a regular expression to parse the format string, and then call the approriate native API according to the parameter type.

Extension to printf

To improve sharing with iOS code, this includes %@ as an acceptable format specificer. Its behavior will match the culture-invariant ToString of the parameter.