Add Makefile check for latex deps

Makefile

@@ -6,12 +6,17 @@ SPHINXOPTS    =
 SPHINXBUILD   = sphinx-build
 PAPER         =
 BUILDDIR      = _build
+LATEXDEPS     = latex dvipng
 
 # User-friendly check for sphinx-build
 ifeq ($(shell which $(SPHINXBUILD) >/dev/null 2>&1; echo $$?), 1)
 $(error The '$(SPHINXBUILD)' command was not found. Make sure you have Sphinx installed, then set the SPHINXBUILD environment variable to point to the full path of the '$(SPHINXBUILD)' executable. Alternatively you can add the directory with the executable to your PATH. If you don't have Sphinx installed, grab it from http://sphinx-doc.org/)
 endif
 
+# check for latex dependencies
+E := $(foreach exec, $(LATEXDEPS),\
+	$(if $(shell which $(exec)), some string,$(error The $(exec) command was not found. Make sure you have LaTeX installed and added to your PATH. If you don't have LaTeX installed, grab it from https://www.latex-project.org/get/)))
+
 # Internal variables.
 PAPEROPT_a4     = -D latex_paper_size=a4
 PAPEROPT_letter = -D latex_paper_size=letter