make ChannelPipeline.init public (#84)
make ChannelPipeline.init public (#84)

Motivation:

There are a few network protocols that are best implemented with child
`Channel`s. And given that those child `Channels` need a
`ChannelPipeline` the init for `ChannelPipeline` should be public.
Otherwise these protocols can only be sensibly implemented in the core
`NIO` module which is unfair.

Modifications:

make `ChannelPipeline.init` public

Result:

modules other than `NIO` can implement child `Channel`s.
apple/swift-nio,apple/swift-nio,apple/swift-nio,apple/swift-nio,apple/swift-nio