Reads bytes from the inner source with the additional ability
to mark a stream at a point that can be returned to later
using the a call to reset(). This reader also makes large, infrequent,
reads to the underlying reader to increase effeciency read, which
ideal when system calls may be involved (e.g., File reads), but offer
little benefit with in-memory readers (e.g., vecs).
Reads bytes from the inner source with the additional ability
to mark a stream at a point that can be returned to later
using the a call to reset(). Whlie the stream is marked all
subsequent reads are returned as usual, but are also buffered,