Makefile: add LUALATEX_PDFS variable, WITH_LUALATEX flag

By default, will not build or clean `BEDv1.pdf`. Use `make
WITH_LUALATEX=1` to add `BEDv1.pdf` to the list of targets in `PDFS`.

This should unbreak the CircleCI build even with an older TeX Live
environment but should be easy to make things work. It's not really
about LuaTeX---what keeps it from working on older TeX Live is
actually packages. But this seems like a better variable name.

In the long run, I suggest:

1. Using recent TeX Live in the CI build image

2. Removing the `WITH_LUATEX` feature flag and always building
`BEDv1.pdf`

3. Switching everything from `pdflatex` to `lualatex` as this is where
the main development of TeX engines is continuing. `lualatex` also has
nice features that `pdftex` lacks such as significantly better Unicode
and font selection support.

Makefile

@@ -2,7 +2,6 @@ all: pdf
 
 PDFS =	BCFv1_qref.pdf \
 	BCFv2_qref.pdf \
-	BEDv1.pdf \
 	CRAMv2.1.pdf \
 	CRAMv3.pdf \
 	crypt4gh.pdf \
@@ -15,6 +14,12 @@ PDFS =	BCFv1_qref.pdf \
 	VCFv4.3.pdf \
 	VCFv4.4.draft.pdf
 
+LUALATEX_PDFS =	BEDv1.pdf
+
+ifdef WITH_LUALATEX
+PDFS += $(LUALATEX_PDFS)
+endif
+
 pdf: $(PDFS:%=new/%)
 
 %.pdf: new/%.pdf