feat(operators): add operators operator

[benlesh]

This adds an operator call operators that enables users to create a new Observable with
operators added to it as methods based on a passed hash of operator methods.

source.operators({ filter, map })
  .filter(x => x > 1)
  .map(x => x * 10)

related #2034

[coveralls]

Coverage increased (+0.007%) to 97.046% when pulling c5b7773 on blesh:withOperator into 7ee0575 on ReactiveX:master.

[benlesh]

I'm proposing this because:

1. I think it solves some of the type inference concerns.
2. It reads a little cleaner and is more ergonomic.
3. Use one method, then other operators would work as normal (but I suppose you could change their names if you choose)
4. It's an alternative

[benlesh]

NOTE: We can move the method to Observable proper like operate from #2034 as well.

[benlesh]

... also the name can be bike-shedded, this is more of a proposal.

[coveralls]

Coverage increased (+0.007%) to 97.046% when pulling 3270253 on blesh:withOperator into 7ee0575 on ReactiveX:master.

[staltz]

Name suggestion: include or including. But still not super happy with the direction this is going.

[lock]

This thread has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.