Added optimized AVX function for sample processing

Added AVX versions of existing 5 SSE functions. Added 6th AVX function to copy vectors which is 1.5 times faster then memcpy.
Data consistency and validness  is fully tested after processing with new AVX functions on aligned and non aligned buffers.

libs/pbd/wscript

@@ -145,6 +145,7 @@ def build(bld):
     if bld.env['build_target'] == 'x86_64':
         obj.defines += [ 'USE_X86_64_ASM' ]
     if bld.env['build_target'] == 'mingw':
+        obj.defines += [ 'NO_POSIX_MEMALIGN' ]
         obj.source += [ 'windows_special_dirs.cc' ]
         obj.uselib += ' OLE'