Place the Makefile variables under their appropriate comments

Author: stevepiercy

Makefile

@@ -1,17 +1,16 @@
 # Makefile for Sphinx documentation
-
 SHELL           = bash
 .DEFAULT_GOAL   = all
 
 # You can set these variables from the command line.
-SPHINXOPTS      =
+SPHINXOPTS      ?=
+PAPER           ?=
+
+# Internal variables.
 SPHINXBUILD     = $(realpath bin/sphinx-build)
 SPHINXAUTOBUILD = $(realpath bin/sphinx-autobuild)
-PAPER           =
 DOCS_DIR        = ./docs/
 BUILDDIR        = ../_build/
-
-# Internal variables.
 PAPEROPT_a4     = -D latex_paper_size=a4
 PAPEROPT_letter = -D latex_paper_size=letter
 ALLSPHINXOPTS   = -d $(BUILDDIR)/doctrees $(PAPEROPT_$(PAPER)) $(SPHINXOPTS) .