Cleaned FindFFMPEG.cmake and fixed use of external FFmpeg lib
#31 Fix search path for external FFmpeg on Linux for multiarch
#31 Fix finding of external FFmpeg libraries for Visual Studio
#31 Fix build of sfeMovie with MinGW
#31 Avoid issues with multiplde FFmpeg include directories
Merge branch '31_ExternalFFmepg' of https://github.com/Yalir/sfeMovie into 31_ExternalFFmepg
Merge branch '31_ExternalFFmepg'