Binlog Stream cannot be disconnected

[galeaspablo]

When retrieving a binlog stream from a connection, the binlog stream has no way of getting disconnected (sending the COM_QUIT signal to MySQL -- not only closing the file handler).

Furthermore, if the stream's connection came from a pool, the pool panics when it gets dropped because its invariants are not respected. Namely, the pool still holds a count from the binlog connection, which it should decrease (but doesn't) when the binlog connection was dropped.

[galeaspablo]

I've made a PR (fully tested). Please see #201

It adds a way to disconnect the binlog stream, and it keeps the pool's invariants when the stream was taken from a pool.

[blackbeam]

#201 merged, so closing. Thanks!