Add ignore-prefix option to no-expression-statement rule

[algesten]

Would you consider a ignore-prefix for the no-expression-statement.

My use case is logging, which pretty much per definition is a side effect, yet something that a server can't really live without. It would clean up my code a lot, since I now have a lot of this going on.

    // tslint:disable-next-line:no-expression-statement
    logSys.error('startup failed', err)

Happy to put a PR together, if you would consider accepting it.

[jonaskello]

Just to clarify you mean that if we configure it like this:

"no-expression-statement": [true, {"ignore-prefix": "sideEffect"}]

Then this would be ignored:

sideEffectFoo("bar")

I think that makes sense and would welcome a PR for it :-).

If the call is a method on an object, I guess then the prefix would apply to the method name and not the object name:

myObj.sideEffectFoo("bar"); // This will be ignored
sideEffectObj.myMethod("bar"); // This will **not** be ignored

Or should both object names and method name be considered?

[algesten]

If the call is a method on an object, I guess then the prefix would apply to the method name and not the object name
...
Or should both object names and method name be considered?

Maybe both? I mean for console.log, would it perhaps be more natural to ignore the whole thing, not just log?