log server events to logFunction

[helfer]

TODO:

• Update CHANGELOG.md with your change (include reference to issue & this PR)
• Make sure all of the significant new logic is covered by tests
• Rebase your changes on master so that they can be merged easily
• Make sure all tests and linter rules pass

[nnance]

So what about a more TypeScript approach:

export enum LogAction {
request, parse, validation, execute
}

export enum LogStep {
start, end
}

export interface LogMessage {
action: LogAction;
step: LogStep;
data?: Object;
}

export interface LogFunction {
(message: LogMessage);
}

export interface QueryOptions {
...
logFunction?: LogFunction;
...
}

Then use it like this:

logFunction({action: LogAction.request, step: LogStep.start});

I know this is more verbose but avoids string matching / parsing and makes it much easier for the consumer. I wouldn't mind making the change to your PR if you like it.