Merge branch 'preprocessor-doc'

doc/preprocessor/Makefile.am

+if HAVE_PDFLATEX
+if HAVE_BEAMER
+pdf-local: preprocessor.pdf
+endif
+endif
+
+SRC = preprocessor.tex expr.png expr-sharing.png matrices.png overview.png json-preprocessor.png
+
+EXTRA_DIST = $(SRC)
+
+preprocessor.pdf: $(SRC)
+	$(PDFLATEX) preprocessor
+	$(PDFLATEX) preprocessor
+
+clean-local:
+	rm -f *.pdf *.toc *.aux *.log *.nav *.snm *.vrb *.out *~

doc/preprocessor/expr-sharing.xml

+<mxfile userAgent="Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:50.0) Gecko/20100101 Firefox/50.0" version="6.0.1.9" editor="www.draw.io" type="device"><diagram name="Page-1">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</diagram></mxfile>
\ No newline at end of file

doc/preprocessor/expr.xml

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\ No newline at end of file

doc/preprocessor/json-preprocessor.xml

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\ No newline at end of file

doc/preprocessor/matrices.xml

+<mxfile userAgent="Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:50.0) Gecko/20100101 Firefox/50.0" version="6.0.1.9" editor="www.draw.io" type="device"><diagram name="Page-1">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</diagram></mxfile>
\ No newline at end of file

doc/preprocessor/overview.xml

+<mxfile userAgent="Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:51.0) Gecko/20100101 Firefox/51.0" version="6.0.2.15" editor="www.draw.io" type="device"><diagram name="Page-1">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</diagram></mxfile>
\ No newline at end of file

doc/preprocessor/readme

+NB: .png files made on https://www.draw.io. They can be edited by loading the .xml file with the same name
+