It's used a lot and it looks a lot like MemoryStore, it just needs not to
return errors from Put and Delete, so make it use MemoryStore internally with
adjusted interface.
Using pointers is just plain wrong here, because the batch can be updated with
newer values for the same keys.
Fixes Seek() to use HasPrefix also because this is the intended behavior.
BoltDB doesn't have internal batching mechanism, thus we have a substitute for
it, but this substitute is absolutely identical to MemoryBatch, so it's better
to unify them and import ac5d2f94d3 fix into the
MemoryBatch.
It must copy both the value and the key because they can be reused for other
purposes between Put() and PutBatch(). This actually happens with values in
headers processing, leading to wrong data being written into the DB.
Extend the batch test to check for that.
add close function to storage interface
add common defer function call which will close db connection
remove context as soon as it's not needed anymore
updated unit tests
