Buttplug Protocol Spec v4 Update

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Buttplug v4 is mainly a refinement of device enumeration from the server to the client, in order to make device information clearer to client developers, and allows them to write simpler and more expressive APIs on top of the protocol.

TODO List:

• Update spec documentation
• Convert DeviceAdded/DeviceList to use Actuators/Sensors instead of message attributes
• Update device configuration to use Actuator/Sensor info instead of message attributes
• Update device configuration loading
• Update device enumeration code to create v4 structures
• Update backward compatibility for v4 -> v3
• Add client v3 tests
• Add client v4 tests
• Remove ActuatorType requirements from ScalarCmd

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Ok, I'll consider the config v2 -> v3 work part of this bug, so can put some discussion here. I don't want to fill up the config discussion with project formatting issues.

@blackspherefollower If you're curious what the new config looks like, check the config-rewrite-minimal branch. I've made separate directories for v2 and v3 config for now, we'll remove v2 once v3 is solidified.

Inheritance still exists in the config, but at the "top" level. Name, description, and features can be overridden, but this time it's an all or nothing thing. v2 allowed overriding per-message, where now if any features change in a specific configuration, all features (even those in the default) must be added to the configuration. The inheritance system has also been completely removed from the configuration code which makes life WAY easier (and all devices are expanded to their full definitions when we load the file). I think simplify things over all.

I wrote a script to convert the v2 yaml to v3, basically filling in all of the missing inheritance values. This seems to have worked, inasmuch as protocol tests pass. That said, it did blow away all of the comments in the v2 file when moving to v3. How much of those do we want to keep around?