Add logging

[lukebakken]

Fixes #81

[lukebakken]

cc @fho

[lukebakken]

I decided to go with the simplest solution and just use the log standard package, without an intermediate interface.

[fho]

Why is logging the errors the right approach to handle them?

If one of those operations fail and cause e.g that a connection becomes unusable this must be either smoothly handled by the package or the error must be forwarded to the user, so the user can react and close the connection.
If a returned error does not cause a problem because e.g. a channel is being closed and the close message can not be send because the connection broke it should be fine to ignore them silently.

[ansd]

I second most (if not all) of the review of @fho

[lukebakken]

Why is logging the errors the right approach to handle them?

I didn't want to change the API of the project at this time. But, maybe I shouldn't worry so much about it.

Thanks @fho and @ansd. I suspect I'll be able to remove the need for logging most or all of these errors by changing the API to ensure errors are returned when appropriate.

[lukebakken]

@fho @ansd OK it turns out that the cases where we were ignoring errors they can in fact be ignored. However, I still would like the ability to turn on logging just in case someone is having a weird issue and logging these places could assist.

Plus, this gives us a starting place should we wish to add very detailed debug logging at some point.

By default logging is not enabled, though it can be via EnableLogger or SetLogger

Requested changes have been addressed.

[fho]

looks great, thank you!

[lukebakken]

Thanks @fho we really appreciate the time you take with this project.