Clean up client exported API

[buchanae]

The client API is probably the most important part of a database's documentation: https://godoc.org/github.com/bmeg/arachne/aql

For AQL there's a bunch of unnecessary junk, such as Register* methods generated by protobuf.

[kellrott]

What is the best way to do this?

[buchanae]

Maybe put the protobuf generated code in an different package, and present the code in aql/query.go as the main query language docs.