* teach the Reader to read heredoc style assignments.
  * add a here-doc.ini file for testing.
  * touch up the reader.t test to make sure it works.
  * add a new block to read_handle that deals with heredocs,
    using the new parse_heredoc_assignment and
    match_heredoc_terminal methods.
* value returned from heredoc's shouldn't have trailing
  newlines.

* touch up wording in test file.
* teach the writer to output strings that contain newlines
  using heredoc format.
  * enhance the tests a bit
  * upgrade the Writer, adding next_heredoc_terminator and
    stringify_value_as_heredoc.