added filetype setting .fx to be recognised as hlsl

e.g vvvv* uses .fx as fileending as convention for effects*  which are (mostly?) shaders

well, i'm not entirely sure if .fx conflicts which any other programming language, this site[3] states .fx is used for direct3d files, so thats a match, i think

sorry i'm not often in the realms of shaders, therefore not entirely sure
i did add the filetype for my own purpose (writing vvvv effects) and maybe it saves one the (super small, but existent) hassle to add it theirselfes

[1] http://vvvv.org/documentation/ex9.hlsl.introduction
[2] http://vvvv.org/documentation/effects
[3] http://file.org/extension/fx