Log Message:
Update drscheme to version 209.
While here, also add the rather useful documentation.

Changes since 207:

Several small errors in the ProfessorJ compiler have been corrected.
Additionally, the native method interface has been updated to
provide more access to class members by the native method.

* The interfaces and implementations for several HtDP and HtDCH
  teachpacks have changed:
  + the World class for HtDCH now supplies 'draw' and 'erase' methods
  + its event callbacks are guaranteed to call erase before and draw
    after handling a tick or keyboard event
  + the world.ss teachpack provides a nw:rectangle function for
    creating rectangles whose pinhole is in the northwest corner.

* Oleg Kiselyov's SSAX/SXML is included in the distribution.

The SSAX/SXML libraries provides functions for reading, writing and
manipulating XML data.  In addition, the package supports the
definition of XML languages and exports machinery for transforming
XML documents based on concise specifications.  SSAX/SXML is the
foundation for a variety of other XML packages in Scheme.  For more
information, see http://ssax.sourceforge.net/ and the documentation
in the "ssax" collection.

* Swindle is now included and maintained with PLT Scheme.

  Swindle is an extension of PLT Scheme.  The main feature is a
  CLOS-like object system based on Tiny-CLOS from Xerox.  Additional
  syntactic extensions include: :keyword values and optional CL-style
  argument lists; syntactic sugar for `define's and `let's; generic
  `set!'; `defsubst' & `letsubst' for defining simple macros,
  `letsyntax', `letsubst' and `letmacro' than can bind identifier
  macros; a list-comprehension macro `list-of' with an extensive
  generic version `collect'; an `echo' mechanism for complex output
  formatting including list iterations; customizing printings via a
  `print-object' generic; `amb', adopted from Dorai's TYSiFD, and
  more.

Like Scheme in DrScheme, Swindle has several language levels.  It is
also possible to use its features on a selective basis.
Those extensions that are not directly related to Tiny CLOS are
likely to migrate into MzLib.