Documentation for FlowHandler

[TurekBot]

Hi,

I'm just learning how to use DataFX. So far, I've found things pretty well documented, and it's been very helpful in learning how DataFX works.

Because I assume a newcomers perspective is valued, I thought I'd mention that I think FlowHandler is, seemingly, an important enough class to deserve some documentation.

Thanks for all the other work you've done so far to provide such a high-quality library. Let me know if there's anything I can do to help.