v6.0.0-beta.0

There's a ton of internal changes an refactorings.

librqbit API might have changed a tiny bit, mostly from newly added options.

Biggest changes:

• streaming API + exposed HTTP endpoint
• librqbit: dynamic storage backends
• ability to write to disk in background with buffering up to certain memory size. Isn't proven useful yet, but may be useful for disks with occasional latency spikes.
• optimisations
• probably new bugs

What's Changed

• Streaming API for existing on-disk storage by @ikatson in #124
• Bump up peer semaphore to increase per-peer speed on high-latency connections by @ikatson in #130
• Dynamic configurable storages by @ikatson in #129
• More storage backends and middlewares + ability to write to storage in background (with a flag / option) by @ikatson in #131
• A lot of changes and refactorings while simulating slow disks by @ikatson in #132

Full Changelog: v5.6.4...v6.0.0-beta.0