Build Reorganization

[juanpedromoreno]

This PR reorganizes packages, sbt modules, and directories, as well as it's improving the naming regarding some of the modules.

Regarding modules renaming:

• mu-rpc-client-core -> mu-rpc-channel: since it's code used in both sides.
• mu-rpc-client-netty -> mu-rpc-netty
• mu-rpc-client-okhttp -> mu-rpc-okhttp

Regarding packages:

Everything under package client is now belonging to channel.

Regarding directories:

• internals contains both internals-fs2 and internals-monix.
• channel contains both netty and okhttp.

[fedefernandez]

We need to update https://github.com/higherkindness/mu/blob/master/docs/src/main/tut/index.md and other docs too with the new module names.

[codecov]

Codecov Report

Merging #518 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #518   +/-   ##
=======================================
  Coverage   81.42%   81.42%           
=======================================
  Files          64       64           
  Lines         985      985           
  Branches       19       19           
=======================================
  Hits          802      802           
  Misses        183      183

Impacted Files	Coverage Δ
...herkindness/mu/rpc/channel/cache/ClientCache.scala	0% <ø> (ø)
...ess/mu/rpc/channel/ManagedChannelInterpreter.scala	100% <ø> (ø)
...main/scala/higherkindness/mu/client/fs2Calls.scala	75% <ø> (ø)
...erkindness/mu/rpc/config/server/ServerConfig.scala	57.14% <ø> (ø)
.../higherkindness/mu/rpc/channel/netty/package.scala	100% <ø> (ø)
...in/scala/higherkindness/mu/server/monixCalls.scala	89.47% <ø> (ø)
...gherkindness/mu/task/instances/TaskInstances.scala	100% <ø> (ø)
...a/higherkindness/mu/rpc/config/server/server.scala	50% <ø> (ø)
...c/main/scala/higherkindness/mu/MonixAdapters.scala	88.46% <ø> (ø)
...higherkindness/mu/rpc/config/channel/channel.scala	100% <ø> (ø)
... and 5 more

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[juanpedromoreno]

Thanks @fedefernandez , let's update that as part of #511 .