Add a "bufferedamountlow" event.

[bemasc]

Fixes #232

[martinthomson]

I think that you want to say that this value starts at zero rather than defaults.

[bemasc]

OK, I've improved the wording here.

[bemasc]

I didn't add an onbufferlow because I think onwhatever is rightly deprecated (and there's no compatibility concern for new events), but if you want to keep parallelism I'm happy to add it.

OK, I've changed the names to bufferedAmountLowThreshold and bufferedamountlow.

[jan-ivar]

@bemasc - Do you have a link about onwhatever being deprecated?

[bemasc]

Mozilla says "If you're working with a modern browser, use addEventListener() instead."

onwhatever has been removed entirely from the DOM Level 2 Events and is never mentioned in the living standard. Admittedly, I haven't found any explicit guidance on whether to include it for new events or not.

[jan-ivar]

Thanks for the link. PeerConnection has onxxx for all its events I think, and AFAIK they were all added after this advice.

[bemasc]

OK, I've added onbufferedamountlow.