Improve windows path aspect implementation

[BurningEnlightenment]

Hello everyone,
The path returned by app_data_path() should point to %USERPROFILE%\AppData\Local, since user specific application data should not be roamed across multiple machines.
Furthermore I simplified the implementation quite a bit, which should make it somewhat faster and easier to maintain. For the latter reason I removed the legacy WinXP code and in addition to that it isn't quite a best-practice to target platforms which aren't supported anymore.

[coveralls]

Coverage increased (+0.44%) to 37.86% when pulling 14cdc44 on BurningEnlightenment:master into b0a419c on retf:master.

[retf]

Hi, thanks for your contribution!

[cnd]

@BurningEnlightenment @retf may you help me with this change

I'm getting following errors now:

e\hdr\application\include\boost/application/detail/windows/path_impl.hpp(90): error C2039: 'SHGetKnownFolderPath' : is not a member of '`global namespace''
e\hdr\application\include\boost/application/detail/windows/path_impl.hpp(90): error C2065: 'KF_FLAG_CREATE' : undeclared identifier
e\hdr\application\include\boost/application/detail/windows/path_impl.hpp(90): error C3861: 'SHGetKnownFolderPath': identifier not found

win 8.1 / msvc 12

[retf]

This is strange, all these symbols are declared in "Shlobj.h" that is included in the path "path_impl.hpp"! @BurningEnlightenment do you can help here! tks!

[BurningEnlightenment]

as I stated I dropped winXP support, so you need to define your NTDDI_VERSION as NTDDI_VISTA or higher.
I usually use this declaration at the beginning of my prefix header file:

#if /* some magic determing the operating system */
#   ifndef _WIN32_WINNT
#       include <winsdkver.h>
#       define _WIN32_WINNT _WIN32_WINNT_WIN7
#       include <SDKDDKVer.h>
#   endif
#endif

please note that you should not define NTDDI_VERSION directly. Furthermore you should ensure that this windows sdk version selection ist done before the inclusion of any windows header file.

[cnd]

@BurningEnlightenment I'm using win 8.1 so detector works wrong somewhere... maybe it will be better to keep XP support for this case?

[BurningEnlightenment]

Your problem is that you didn't define the version of the windows SDK you want to use and the default still seems to be winXP. What we can do is to introduce some preprocesor magic which ensures a minimum windows sdk version and produces a helpful error message.

[cnd]

@BurningEnlightenment that will force many people to include that prefix header to each codebase but maybe it's right.

[BurningEnlightenment]

so I created WinSdkVerVista.h which does the version selection and should be included before every win sdk header at least once if you didn't roll your own win sdk version selection solution.
Furthermore I added an #error to path_impl.h which describes the thing and points to the file above. @retf is this sufficient? And if it is I encourage you to pull those additions ;)

[retf]

Hi, I dont know if many users of Applicatio uses XP, anyway, send a pull! I will add it!