expose dowloadFromInfo and drop some dependencies

This pull request:

 * retains backward compatibility
 * removes request caching. Instead you are supposed to use `getInfo` followed by `downloadFromInfo`.
 * drops dependency on eventvat
 * drops dependency on streamify, uses built-in `PassThrough` stream instead.

All tests pass.
The thing with this now is that it creates 2 PassThrough streams, which seems unnecessary.

We can export a different downloading from info function that calls `downloadFromInfo()`, and that creates the PassThrough stream.