Adopt DispatchWorkItem for scheduling tasks

[minuscorp]

Adopt DispatchWorkItem for better Foundation, Dispatch and NIO interoperability.

Breaking changes:

• reducerGroup does not depend on RxSwift anymore, so for managing subscriptions we use a Combine-like approach, where the Cancelables are just added to a [Cancelable] that can be cleaned up removeAll() or just released on deinit

[sebastianvarela]

SwiftLint found issues

Warnings

File	Line	Reason
DispatcherTests.swift	47	Types should be nested at most 1 level deep (nesting)
ObservableTypeTests.swift	15	Variable name should be between 3 and 40 characters long: 'by' (identifier_name)
ObservableTypeTests.swift	34	Method 'setUp()' should call to super function (overridden_super_call)
ObservableTypeTests.swift	47	Collection literals should not have trailing commas. (trailing_comma)
ObservableTypeTests.swift	58	Collection literals should not have trailing commas. (trailing_comma)

Errors

File	Line	Reason
ReducerTests.swift	20	Variable name should only contain alphanumeric characters: '_counter' (identifier_name)
ReducerTests.swift	52	Variable name should only contain alphanumeric characters: '_counter' (identifier_name)
ReducerTests.swift	76	Variable name should only contain alphanumeric characters: '_counter' (identifier_name)
ReducerTests.swift	106	Variable name should only contain alphanumeric characters: '_counter' (identifier_name)
ReducerTests.swift	133	Variable name should only contain alphanumeric characters: '_counter' (identifier_name)

Generated by :no_entry_sign: Danger

[sebastianvarela]

@minuscorp Please, this PR is outdated and i want to unsubscribe from them. You can close this? :D

[minuscorp]

Why is this outdated, also, if notifications bother you, you can choose to unwatch for changes on it. This approach was tested and valid, but none reviewed it before I left.