moved multiwriter to writer and updated to use NewWriter

Moving Example (multi) to the example_writer_test file
actually tests and shows the output properly in godoc.
This change also uses the new NewWriter function signature as opposed to Writer.
Exports Writer, changed API for creating a writer

Changed Writer function to NewWriter to be more idiomatic.
Also export Writer struct so that godoc and callees can see the
SetDelay and Write functions.