Convert man page to AsciiDoc.

Signed-off-by: Lukas Fleischer <calcurse@cryptocrack.de>

doc/Makefile.am

@@ -5,12 +5,24 @@ ASCIIDOC_ARGS = \
 	-a toc \
 	-a icons
 
+A2X_ARGS = \
+	-d manpage \
+	-f manpage
+
 doc_DATA = \
 	manual.html
 
+man_MANS = \
+	calcurse.1
+
 docdir = $(datadir)/doc/$(PACKAGE)
 
 .txt.html:
 if HAVE_ASCIIDOC
 	$(AM_V_GEN) $(ASCIIDOC) $(ASCIIDOC_ARGS) $<
 endif
+
+calcurse.1: calcurse.1.txt
+if HAVE_A2X
+	$(AM_V_GEN) $(A2X) $(A2X_ARGS) $<
+endif