Doc: do not rely on checked-out Sphinx toolchain from svn.python.org anymore

Nowadays it is likely that people will have Sphinx installed,
and if not, they will know how to install it.

This also simplifies life a lot for distribution packagers,
who typically do not want the doc build process to connect
to external web resources.
diff --git a/Doc/Makefile b/Doc/Makefile
index 82f5bef..4734526 100644
--- a/Doc/Makefile
+++ b/Doc/Makefile
@@ -5,7 +5,7 @@
 
 # You can set these variables from the command line.
 PYTHON       = python
-SVNROOT      = http://svn.python.org/projects
+SPHINXBUILD  = sphinx-build
 SPHINXOPTS   =
 PAPER        =
 SOURCES      =
@@ -21,7 +21,6 @@
 help:
 	@echo "Please use \`make <target>' where <target> is one of"
 	@echo "  clean      to remove build files"
-	@echo "  update     to update build tools"
 	@echo "  html       to make standalone HTML files"
 	@echo "  htmlhelp   to make HTML files and a HTML help project"
 	@echo "  latex      to make LaTeX files, you can set PAPER=a4 or PAPER=letter"
@@ -37,30 +36,8 @@
 	@echo "  check      to run a check for frequent markup errors"
 	@echo "  serve      to serve the documentation on the localhost (8000)"
 
-# Note: if you update versions here, do the same in make.bat and README.txt
-checkout:
-	@if [ ! -d tools/sphinx ]; then \
-	  echo "Checking out Sphinx..."; \
-	  svn checkout $(SVNROOT)/external/Sphinx-1.2/sphinx tools/sphinx; \
-	fi
-	@if [ ! -d tools/docutils ]; then \
-	  echo "Checking out Docutils..."; \
-	  svn checkout $(SVNROOT)/external/docutils-0.11/docutils tools/docutils; \
-	fi
-	@if [ ! -d tools/jinja2 ]; then \
-	  echo "Checking out Jinja..."; \
-	  svn checkout $(SVNROOT)/external/Jinja-2.3.1/jinja2 tools/jinja2; \
-	fi
-	@if [ ! -d tools/pygments ]; then \
-	  echo "Checking out Pygments..."; \
-	  svn checkout $(SVNROOT)/external/Pygments-1.6/pygments tools/pygments; \
-	fi
-
-update: clean checkout
-
 build: checkout
-	mkdir -p build/$(BUILDER) build/doctrees
-	$(PYTHON) tools/sphinx-build.py $(ALLSPHINXOPTS)
+	$(SPHINXBUILD) $(ALLSPHINXOPTS)
 	@echo
 
 html: BUILDER = html
@@ -120,10 +97,6 @@
 
 clean:
 	-rm -rf build/*
-	-rm -rf tools/sphinx
-	-rm -rf tools/pygments
-	-rm -rf tools/jinja2
-	-rm -rf tools/docutils
 
 dist:
 	rm -rf dist