Consider Exposing EBML Parsing Logic

[brycefisher]

I'm trying to parse matroska containers to get at the encoded video bitstreams within the file. It seems like this library doesn't expose any of the element sizes or byte offsets, and that doing so would probably defeat the purpose of this library.

Would you be open to receiving a PR to:

1. separate out the EBML parsing bits into a separate crate, OR
2. publicly reexport the ebml.rs functionality so that I could consume it directly as part of this crate

I'm guessing that work is fairly trivial, and if you're willing to accept a PR for one of these approaches, I'd being to dedicate an hour or two towards making that happen. (Also, I totally understand if this is not in the direction you want to go here.) Thanks!!

[brycefisher]

Actually, after looking at the mkv crate, it seems like this library does exactly what I'm looking for already. I'm going to close this issue in favor of using that library.