formatting, mostly
moved DLL functionality partly into a separate class
sadly, porting CustomFunctionBase<function_type>::loadFunction() to FunctionDLL instead of dlopen()/dlsym() does not work easily. Dunno why. Committing it as it is now. (#22)
cleaned up some of the preset plugins
fixed crash when loading a function from a FunctionDLL object. why the fix works is still mysterious for me though. (#22)