#104 avisynth_c interface not require declspec

[Steven Walters]

I wish to use the avisynth_C interface, but do not desire to link with declspec with it's side effect of preventing program execution if avisynth.dll is not available.
I have created a patch to allow avisynth_C.h to be used without declspec(dllimport) linking and provide some new inline functions for expediting the use of the library through the LoadLibrary, GetProcAddress, and FreeLibrary methods.

I am willing to take feedback and continually process to bring this up to the maintainers' standards.
But I would really see a benefit if someone could use avisynth without requiring declspec and not resorting to hack-like workarounds to perform such linking.

[Steven Walters]

patch file