Support for throttleProp

[wuct]

Please see #168 for more detail

[wuct]

I do not think this is a good idea to introduce xforms here, because xforms is designed for internal use in createHocFromMiddleware and might be changed in the future.
However, it is just a quick hack and advices are welcome.

[acdlite]

Cool! (Heads up, I probably won't be able to review this until next week when I get back from React Europe.)

[wuct]

@acdlite Good luck on your talk and workshop ;)
I wish I could be there.

[istarkov]

@wuct having mapPropsStream do we need throttleProps?

[wuct]

@istarkov IMHO it still need time for Observable to get widely-adopted, so throttleProps might be still useful.

However, mapPropsStream can replace all other functions in the end.

[jschlieber]

When can we expect this feature to be released?

[wuct]

@jschlieber Because this PR is blocked by #182, the time is still uncertain.

[istarkov]

Will close as corresponding or is also closed, and it looks to me that its always better to throttle handlers and not props as like as here https://github.com/deepsweet/hocs