Add `Result` wrapper when querying

Right now, the result of queries like TS.RANGE is an array of value objects. To make this more user-friendly for using the raw data (e.g. displaying on a chart), it would be nice to return a Redis::TimeSeries::Result wrapper to hold those value objects, and provide convenience wrappers for converting them into hashes and arrays.

[9] pry(main)> result
=> [#<Redis::TimeSeries::Sample:0x00007f803088b7f8 @time=2020-06-29 23:43:12 -0700, @value=0.1e1>,
 #<Redis::TimeSeries::Sample:0x00007f803088b640 @time=2020-06-29 23:43:12 -0700, @value=0.2e1>,
 #<Redis::TimeSeries::Sample:0x00007f803088b488 @time=2020-06-29 23:43:12 -0700, @value=0.3e1>]

# Could return 2d array/hash of times and values (Time object probably more useful elsewhere in a Ruby app)
[10] pry(main)> result.map { |r| [r.time, r.value] }
=> [[2020-06-29 23:43:12 -0700, 0.1e1], [2020-06-29 23:43:12 -0700, 0.2e1], [2020-06-29 23:43:12 -0700, 0.3e1]]
[11] pry(main)> result.to_h { |r| [r.time, r.value] }
=> {2020-06-29 23:43:12 -0700=>0.1e1, 2020-06-29 23:43:12 -0700=>0.2e1, 2020-06-29 23:43:12 -0700=>0.3e1}

# Or, convert to raw milliseconds first (closer to raw reply from Redis)
[12] pry(main)> result.map { |r| [r.time.ts_msec, r.value] }
=> [[1593499392263, 0.1e1], [1593499392276, 0.2e1], [1593499392298, 0.3e1]]
[13] pry(main)> result.to_h { |r| [r.time.ts_msec, r.value] }
=> {1593499392263=>0.1e1, 1593499392276=>0.2e1, 1593499392298=>0.3e1}