Add more proto documentation

[2qx]

Add more explanatory documentation to protoc methods, types and fields.

• Makes no change to the protocol itself.
• Adds specificity for terms used to refer to many things,
• Adds synonyms for words used interchangeably
• Aims to provides an outside audience a succinct explanation,
  or enough key terms to obtain more information elsewhere.
• Note quirks and defaults, where possible.

[cpacia]

Thanks for the PR. Will take a look shortly.

[cpacia]

@2qx any chance you can update the method comments in bchrpc/server.go to match the new comments in the proto file?

[2qx]

Will do.

[2qx]

@cpacia, I matched the comments from the proto.

In addition, there were some trailing whitespace in the protofile and some whitespace lines that I removed from the proto for consistency with go fmt.

[zquestz]

Thanks this looks great!