doc: Make build system insert version in Doxyfile

configure.ac

@@ -1157,6 +1157,7 @@ AC_SUBST(QR_LIBS)
 AC_CONFIG_FILES([Makefile src/Makefile doc/man/Makefile share/setup.nsi share/qt/Info.plist test/functional/config.ini])
 AC_CONFIG_FILES([test/util/buildenv.py],[chmod +x test/util/buildenv.py])
 AC_CONFIG_FILES([contrib/devtools/split-debug.sh],[chmod +x contrib/devtools/split-debug.sh])
+AC_CONFIG_FILES([doc/Doxyfile])
 AC_CONFIG_LINKS([test/functional/test_runner.py:test/functional/test_runner.py])
 AC_CONFIG_LINKS([test/util/bitcoin-util-test.py:test/util/bitcoin-util-test.py])
 AC_CONFIG_LINKS([test/util/bctest.py:test/util/bctest.py])

doc/Doxyfile.in

@@ -38,7 +38,7 @@ PROJECT_NAME           = "Bitcoin Core"
 # could be handy for archiving the generated documentation or if some version
 # control system is used.
 
-PROJECT_NUMBER         = 0.14.99
+PROJECT_NUMBER         = @PACKAGE_VERSION@
 
 # Using the PROJECT_BRIEF tag one can provide an optional one line description
 # for a project that appears at the top of each page and should give viewer a