initialize a RegretableReader with underlying reader r.

initialize a RegretableReaderCloser with underlying readCloser rc.

initialize a RegretableReaderCloser with underlying readCloser rc.

initialize a RegretableReader with underlying reader r, whose buffer is size bytes long.

A RegretableReader will allow you to read from a reader, and then to "regret" reading it, and push back everything you've read.

Same as RegretableReader, but allows closing the underlying reader.