Additions to WinApi

[klemens-morgenstern]

I removed all direct inclusions of windows.h in boost/process and replaced them in the boost.winapi style. I hope this library would be the right place for those additions, so boost.process can use them.

[Lastique]

I had a quick look and unfortunately I cannot accept this PR in its current form. Here are some comments:

• All new files must have a proper copyright and license note.
• No __declspec and raw types in the declarations. Use the corresponding macros and typedefs.
• No function declarations that are actually macros in the Windows SDK. This mostly concerns functions that accept strings. For each such function there should be two declarations (*A and *W), the narrow one should be conditioned on BOOST_NO_ANSI_APIS. Where appropriate, there can be a lower-case overload that calls the correct function depending on the argument types.
• When windows.h is not included all functions must be declared in the global namespace. When no type punning is required, the functions can be simply imported into boost::detail::winapi. Otherwise, there should be an inline wrapper function in boost::detail::winapi that performs type conversions and calls the real function in the global namespace.
• All constants should be declared with the same case as the original constants in Windows SDK, with an underline appended. E.g. const DWORD_ DEBUG_PROCESS_ = DEBUG_PROCESS;. The lower-case versions are optional and are provided in addition to the upper-case ones, where possible (e.g. when they don't clash with something else).
• No extern "C" in boost::detail::winapi.
• All structures must be re-defined in boost::detail::winapi in an ABI-compatible way to the originals in Windows SDK. When windows.h is not included, the original structs must be forward-declared in the global namespace. When a struct is involved in a function interface, the inline wrapper in boost::detail::winapi for the function must be present.
• No dependency on UNICODE, please. All structs must have stable implementation regardless of the macros.
• No TCHAR, please. It should not exist.
• There's no DWOD_ type (see show_windows.hpp). Run the tests first, please.
• Actually, I'm not sure I like that show_windows.hpp adds constants that seem to be related to the windowing system to Boost.WinAPI. I'm not sure this is the right place for them.

All in all, have a look at the other headers in Boost.WinAPI and try to follow the existing practice.

[klemens-morgenstern]

Thank you for the comments. I'll incorporate your comments and hopefully it'll be a better PR next time.