Make PKGDOCDIR configurable for distributions.

--- a/configure.ac	2018-07-08 12:35:56.000000000 +0200
+++ b/configure.ac	2019-03-10 20:11:45.053432800 +0100
@@ -227,7 +227,7 @@
 
 # Other defines
 AC_DEFINE_UNQUOTED(PKGLIBDIR,"$prefix/share/calf/",[Calf shared data directory (bitmaps, GUI XML etc.)])
-AC_DEFINE_UNQUOTED(PKGDOCDIR,"$prefix/share/doc/calf/",[Calf documentation directory])
+AC_DEFINE_UNQUOTED(PKGDOCDIR,"$htmldir",[Calf documentation directory])
 
 ############################################################################################
 
--- a/Makefile.am	2018-07-08 12:35:56.000000000 +0200
+++ b/Makefile.am	2019-03-10 20:55:12.448824164 +0100
@@ -25,29 +25,29 @@
 	rm -rf autom4te.cache
 
 install-data-local:
-	install -d -m 755 $(DESTDIR)$(docdir)
-	install -d -m 755 $(DESTDIR)$(docdir)/images
-	install -d -m 755 $(DESTDIR)$(docdir)/images/icons
-	install -d -m 755 $(DESTDIR)$(docdir)/images/prettyPhoto
-	install -d -m 755 $(DESTDIR)$(docdir)/images/prettyPhoto/dark_rounded
-	install -d -m 755 $(DESTDIR)$(docdir)/scripts
+	install -d -m 755 $(DESTDIR)$(htmldir)
+	install -d -m 755 $(DESTDIR)$(htmldir)/images
+	install -d -m 755 $(DESTDIR)$(htmldir)/images/icons
+	install -d -m 755 $(DESTDIR)$(htmldir)/images/prettyPhoto
+	install -d -m 755 $(DESTDIR)$(htmldir)/images/prettyPhoto/dark_rounded
+	install -d -m 755 $(DESTDIR)$(htmldir)/scripts
 	install -d -m 755 $(DESTDIR)$(pkgdatadir)/sf2
-	install -c -m 644 $(top_srcdir)/doc/manuals/*.html $(DESTDIR)$(docdir)
-	install -c -m 644 $(top_srcdir)/doc/manuals/images/*.png $(DESTDIR)$(docdir)/images/
-	install -c -m 644 $(top_srcdir)/doc/manuals/images/*.jpg $(DESTDIR)$(docdir)/images/
-	install -c -m 644 $(top_srcdir)/doc/manuals/images/prettyPhoto/dark_rounded/* $(DESTDIR)$(docdir)/images/prettyPhoto/dark_rounded/
-	install -c -m 644 $(top_srcdir)/doc/manuals/images/icons/* $(DESTDIR)$(docdir)/images/icons/
-	install -c -m 644 $(top_srcdir)/doc/manuals/scripts/*.css $(DESTDIR)$(docdir)/scripts/
-	install -c -m 644 $(top_srcdir)/doc/manuals/scripts/*.js $(DESTDIR)$(docdir)/scripts/
+	install -c -m 644 $(top_srcdir)/doc/manuals/*.html $(DESTDIR)$(htmldir)
+	install -c -m 644 $(top_srcdir)/doc/manuals/images/*.png $(DESTDIR)$(htmldir)/images/
+	install -c -m 644 $(top_srcdir)/doc/manuals/images/*.jpg $(DESTDIR)$(htmldir)/images/
+	install -c -m 644 $(top_srcdir)/doc/manuals/images/prettyPhoto/dark_rounded/* $(DESTDIR)$(htmldir)/images/prettyPhoto/dark_rounded/
+	install -c -m 644 $(top_srcdir)/doc/manuals/images/icons/* $(DESTDIR)$(htmldir)/images/icons/
+	install -c -m 644 $(top_srcdir)/doc/manuals/scripts/*.css $(DESTDIR)$(htmldir)/scripts/
+	install -c -m 644 $(top_srcdir)/doc/manuals/scripts/*.js $(DESTDIR)$(htmldir)/scripts/
 	install -c -m 644 $(top_srcdir)/sf2/*.sf2 $(DESTDIR)$(pkgdatadir)/sf2/
 	    
 uninstall-local:
-	rm -f $(DESTDIR)$(docdir)/*.html
-	rm -f $(DESTDIR)$(docdir)/images/*.png
-	rm -f $(DESTDIR)$(docdir)/images/*.jpg
-	rm -f $(DESTDIR)$(docdir)/images/icons/*.png
-	rm -f $(DESTDIR)$(docdir)/images/prettyPhoto/dark_rounded/*
-	rm -f $(DESTDIR)$(docdir)/scripts/*.css
-	rm -f $(DESTDIR)$(docdir)/scripts/*.js
+	rm -f $(DESTDIR)$(htmldir)/*.html
+	rm -f $(DESTDIR)$(htmldir)/images/*.png
+	rm -f $(DESTDIR)$(htmldir)/images/*.jpg
+	rm -f $(DESTDIR)$(htmldir)/images/icons/*.png
+	rm -f $(DESTDIR)$(htmldir)/images/prettyPhoto/dark_rounded/*
+	rm -f $(DESTDIR)$(htmldir)/scripts/*.css
+	rm -f $(DESTDIR)$(htmldir)/scripts/*.js
 	rm -f $(DESTDIR)$(pkgdatadir)/sf2/*.sf2
-	rmdir $(DESTDIR)$(docdir)/scripts $(DESTDIR)$(docdir)/images/icons $(DESTDIR)$(docdir)/images/prettyPhoto/dark_rounded $(DESTDIR)$(docdir)/images/prettyPhoto $(DESTDIR)$(docdir)/images $(DESTDIR)$(docdir) $(DESTDIR)$(pkgdatadir)/sf2 || true
+	rmdir $(DESTDIR)$(htmldir)/scripts $(DESTDIR)$(htmldir)/images/icons $(DESTDIR)$(htmldir)/images/prettyPhoto/dark_rounded $(DESTDIR)$(htmldir)/images/prettyPhoto $(DESTDIR)$(htmldir)/images $(DESTDIR)$(htmldir) $(DESTDIR)$(pkgdatadir)/sf2 || true