Create non-owning IO-buffer

[harsath]

Right now, the blueth::IOBuffer which does the non-blocking async networking IO is implemented using a owning buffer, which means, if we pass a memory location with it's size, it copies the entire memory block and owns it.

It's a fine process, but it makes copies(which is good, but sometimes bad and hurts performance in cases where copies are trivially not needed).

Let's create a non-owining Mutable and ReadOnly buffers buffer, we expect one to pass the pointer to the memory location and with it's size and we do the operations on the pointer.

• Mutable Buffer
  We expect one to pass a pointer to a memory block which is managed by some other thing, with the current_capacity, current_offset and start_pointer
• Read Only Buffer
  We expect one to pass a pointer to a memory block which is again managed by some other thing, we assume that the life time of the memory block is managed by the thing which created the Read Only Buffer.