Makefile: add REHL coloring (only if available)

Makefile

@@ -8,11 +8,18 @@
 
 export TEXINPUTS=.:liu-beamer-libre/tex/latex/liu/liuslides:liu-beamer-libre/tex/generic/images/logo/liu_eng:
 
+# REHL LaTeX output coloring, if available
+ifeq (, $(shell which rehl))
+LATEXMK_FILTER=cat
+else
+LATEXMK_FILTER=rehl -r '[Ee]rrors?:?' -y '[Ww]arnings?:?' -p '[\w\d_\-\.]+\.((pdf)|(tex)|(png)|(svg))'
+endif
+
 main.pdf: main.tex
-	latexmk -pdf -pdflatex="lualatex -synctex=1 -halt-on-error" -use-make $<
+	latexmk -pdf -pdflatex="lualatex -synctex=1 -halt-on-error" -use-make $< | ${LATEXMK_FILTER}
 
 keep-going: main.tex
-	latexmk -pdf -pvc -pdflatex="lualatex -synctex=1 -halt-on-error" -use-make $<
+	latexmk -pdf -pvc -pdflatex="lualatex -synctex=1 -halt-on-error" -use-make $< | ${LATEXMK_FILTER}
 
 clean:
 	@rm -fv *.aux *.fdb_latexmk *.fls *.log *.synctex.gz *.blg *.bbl *.nav *.snm *.out *.toc *.vrb