ApplyDelta builds thew new file.

NewReaderIteratorBuffer creates an iterator, referencing an already-allocated buffer that will read until EOF.

NewReaderIteratorBufferNBytes creates an iterator that will stop after reading `nBytesToRead` bytes, referencing an already-allocated buffer.

NewReaderIteratorSize creates an iterator, allocating a buffer of `bufferSize`.

NewReaderIteratorSize creates an iterator, allocating a buffer of `bufferSize`.

ReaderIterator lets you treat reading bytes from an io.Reader as a for-loop.