[5.0] monitorDisconnection on Peripheral instance should return the error to the user

[Kacper20]

Currently method signature for monitorDisconnection looks as follows:
public func monitorDisconnection(for peripheral: Peripheral) -> Observable<Peripheral>
Delegate callback that is used to implement this contains additional information regarding the error which is currently ommited by our library.

Design

Ideally we would change the interface to the following one:

typealias DisconnectionReason = Error?
public func monitorDisconnection(for peripheral: Peripheral) -> Observable<(Peripheral, DisconnectionReason)>

How it affects current users

It’s a source breaking change and should be a part of 5.0 release.

[Kacper20]

Implemented in #175 Thanks @bartoszstelmaszuk!