Request: Dividend yield API endpoint.

[Dionamus]

I know that this can be done with two API requests (I'm currently using /v3/reference/dividends and /v2/aggs/grouped/locale/us/market/stocks/{date} with funky date math like I mentioned in #36) and just dividing the dividend (and optionally multiply the frequency) by the price, but if such an endpoint existed, it could also be done with just one.

I'd also include parameters for specifying forward yield and trailing twelve months (TTM).