Support compression

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No description provided.

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Small progress update

Legacy protocol uses ZLIB encoded data for each message as per clue/reactphp-zlib#16 and is rather straight-forward.

DataStream protocol uses a streaming ZLIB compression on the message stream as per https://github.com/quassel/quassel/blob/68878dc8366f2f4a0afe132847aad9a51a80cdbf/src/common/compressor.cpp#L239 and https://github.com/quassel/quassel/blob/68878dc8366f2f4a0afe132847aad9a51a80cdbf/src/common/remotepeer.cpp#L265.

The legacy compression is ready, but the protocol is hardly in use today. The newer DataStream protocol depends on a streaming ZLIB compressor first, so we'll need to address clue/reactphp-zlib#4 first.

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Just a quick dump to show what kind of impact this had back when I looked into this:

uncompressed legacy: 1407823 bytes (~66s)
compressed legacy: 125462 bytes (~3s)

uncompressed datastream: 589873 bytes (~10s)
compressed datastream: unknown, but estimated to be < 100 KB

These numbers were measured a while back for only the initial handshake and network sync. The times were measured before introducing #26, so I do not expect such a significant change except for transfer times anymore.