COMPAT: Repair for 5/23/18 IEX Update

[addisonlynch]

Summary (include Python version)

The provider updated a few endpoints on May 23, 2018 (see IEX Docs).

The following will need to be changed and/or updated:

Add /largest-trades endpoint
Add chartLast and changeFromClose parameters to /stock/chart
Add extendedPrice, extendedChange, extendedChangePercent and extendedPriceTime to
/stock/quote
Add yearAgo, yearAgoChangePercent, estimatedChangePercent and symbolId
to /stock/earnings
Updated Attribution section of docs. Simplified attribution by removing second step.
Corrected /stock/chart section of docs. Corrected date format for 1d. Updated return value
coverage.

Date/time of issue

Expected behavior

Actual behavior