Generate man pages from asciidoc

Working directly with g/roff is a pain.
Also changed the formatting of toxic.conf.5 a bit.

Signed-off-by: Loui Chang <louipc.ist@gmail.com>

cfg/targets/help.mk

@@ -3,6 +3,7 @@ help:
 	@echo "-- Targets --"
 	@echo "  all:     Build toxic [DEFAULT]"
 	@echo "  toxic:   Build toxic"
+	@echo "  doc:     Build documentation"
 	@echo "  install: Build toxic and install it in PREFIX (default PREFIX is \"$(abspath $(PREFIX))\")"
 	@echo "  clean:   Remove built files"
 	@echo "  help:    This help"