Improve Redis internal function signatures for hashes, other data structures (HGETALL, etc.) #820
Description
This issue requires modifying https://github.com/etsy/phan/blob/master/src/Phan/Language/Internal/FunctionSignatureMap.php
Also see https://github.com/phpredis/phpredis#classes-and-methods and https://redis.io/commands
Current status: hgetall, etc could be more specific (typically array<string,string>, not array.