this should simplify building SciTECO for new users

 * compiler and archiver are passed down from Autoconf,
   so cross-compiling should work transparently
 * `make clean` will also clean the Scintilla source tree
 * there is no longer any need for "source bundles" as
   tar balls also contain Scintilla/Scinterm now
 * building from Git is not much more difficult than building
   from a tar ball
 * The versions of Scintilla/Scinterm embedded as submodules
   already contain all the patches necessary (currently none are
   necessary), so there's no need to have patch files in the
   repository
 * INSTALL instructions have been rewritten
 * the --with-scintilla and --with-scinterm site-config options
   have been kept. But they should be rarely necessary now.

 * this allows us to remove the last patch to the Scintilla/Scinterm code
   base (for the time being at least)

 * allows us to remove most patches. One however is still necessary
   (Scinterm Makefile bug!)
 * TECO-style control code echoing is now set up using the SCI_SETREPRESENTATION message
 * updated copyrights
 * updated TODO

 * MinGW binaries are built from source bundles
 * patches are applied to the source bundle
 * so all necessary patches must be in the repository and distributed
 * use a leading number in patch names to ensure proper application order

in the future, I might submit a more elaborate Scintilla patch for configuring
the control code strings.