Add support for streams / pipes

[skerit]

I love the simplicity of your avconv library, but I was sorely lacking support for pipe:0 input and pipe:1 output.

This commit adds that.

All the informational data is now emitted as a 'message' event,
while the converted data is now using the 'data' event.

The 'end' event has also been renamed to 'exit', because the 'end' event makes the stream unreadable.

[binarykitchen]

Very nice @skerit, that's a great change! I added few comments here and there. Looking forward to your next round. And please, if you do not mind, please merge all the commits into a single one.

Just curious, why do you need pipe:0 and pipe:1 when you already can pass on the input via parameters with the current version?

[skerit]

Alright, I took all the comments and fixed them. I squashed my commits into 1 single commit, which removed all the original comments and my response to them, though :/
Do you still have the mails of github?

Do you mean: why would you want to use pipes instead of regular files?

I need it for on-the-fly streaming of the converted data to browsers and such. And I need to do it with the least amount of latency as possible, so... :)

[binarykitchen]

Wonderful, thanks for the changes. Merged. I will do few more changes and publish to npm soon.

Ummm, you make me curious regarding "on-the-fly" streaming? What's your current project and where do you need that feature? The reason why I am asking is because I am working on https://videomail.io ... have a look!