Ring buffer data structures

[harendra-kumar]

Make ring buffer a first class streaming citizen by providing read unfold and write fold for it just like array. That will enable us to use ringbuffers more e.g. lastN can actually return a ringbuffer instead of array.

[harendra-kumar]

PR #1340 added signatures for the ring buffer APIs. Let's implement those.

[adithyaov]

This will also require extensive testing.

[adithyaov]

Ring buffer user-facing APIs

Currently, the user-facing APIs of the ring buffer are not very safe. It's very
easy to shoot yourself in the foot when uninitialized elements are involved.

The internal representation can be extended to keep track of things
like ringLength, ringHead, etc.

Possibly,

data Ring a = Ring
    { ringContents :: {-# UNPACK #-} !MutByteArray
    , ringHead :: {-# UNPACK #-} !Int     -- ^ Write index
    , ringTail :: {-# UNPACK #-} !Int     -- ^ Read index
    , ringLength :: {-# UNPACK #-} !Int   -- ^ Buffer length
    , ringCapacity :: {-# UNPACK #-} !Int -- ^ Buffer capacity
    }

[adithyaov]

This can be closed. Most of the ring changes have been merged into master.
See: #2832