Add fprintf overload that writes to a std::ostream

For completeness, add an overload for printf that takes a std::ostream.

Reduce compile time of variadic functions (2)

for consistency with used coding conventions.

Declarations for shared library in Windows.

Added __declspec(dllimport) and __declspec(dllexport) declarations
when compiled in Windows.

because the memory areas may overlap.

~20% faster compile time on bloat-test

Fix fileno causing compile error when #defined

Error:
expected unqualified-id before '(' token
 int fmt::BufferedFile::fileno() const {

This is an issue with Android NDK and mingw32.

and improve naming consistency

Silence some performance warnings in Visual Studio

Older Visual Studio versions are not shipped with stdint.h