* Introduce Group interface and AllGroup
As we move towards consumer groups we'll need to support the current
"consume all shards" strategy, and setup the codebase for the
anticipated "consume balanced shards."
* Use shard broker to start processing new shards
The addition of a shard broker will allow the consumer to be notified
when new shards are added to the stream so it can consume them.
Fixes: https://github.com/harlow/kinesis-consumer/issues/36
Major changes:
```go
type ScanFunc func(r *Record) error
```
* Simplify the callback func signature by removing `ScanStatus`
* Leverage context for cancellation
* Add custom error `SkipCheckpoint` for special cases when we don't want to checkpoint
Minor changes:
* Use kinesis package constants for shard iterator types
* Move optional config to new file
See conversation on #75 for more details
Having an additional Client has added some confusion (https://github.com/harlow/kinesis-consumer/issues/45) on how to provide a
custom kinesis client. Allowing `WithClient` to accept a Kinesis client
it cleans up the interface.
Major changes:
* Remove the Client wrapper; prefer using kinesis client directly
* Change `ScanError` to `ScanStatus` as the return value isn't necessarily an error
Note: these are breaking changes, if you need last stable release please see here: https://github.com/harlow/kinesis-consumer/releases/tag/v0.2.0
The Checkpoint functionality is an important part of the library and
previously it wasn't obvious that the Consumer was defaulting to Redis
for this functionality.
* Add Checkpoint as required param for new consumer
Major changes:
* Remove intermediate batching of kinesis records
* Call the callback func with each record
* Use functional options for config
https://dave.cheney.net/2014/10/17/functional-options-for-friendly-apis
Minor changes:
* update README messaging about Kinesis -> Firehose functionality
* remove unused buffer and emitter code
