Fix several URLs in documentation parts

We have no longer svn, but 2 doxygen branches.
I don't remember, when Mailman moved from www to lists.

bindings/python/example_scripts/gncinvoice_jinja.py

@@ -22,7 +22,7 @@
 # more modular as it allows to use arbitrary templates
 #
 # Doxygen docs:
-# - http://svn.gnucash.org/docs/HEAD/
+# - https://code.gnucash.org/docs/MAINT or MASTER
 # - see page \ref py_invoice_export
 #
 # Questions / Issues:

bindings/python/example_scripts/latex_invoices.py

@@ -28,7 +28,7 @@
 #
 # Additional information :
 #
-# - Doxygen docs: see page \ref py_invoice_export at http://svn.gnucash.org/docs/HEAD/
+# - Doxygen docs: see page \ref py_invoice_export at https://code.gnucash.org/docs/MAINT or MASTER
 # - http://www.uweziegenhagen.de/latex/documents/rechnung/rechnungen.pdf (german)
 #
 # Credits to and ideas from