ltlcross: follow RFC 4180 for CSV output.

* src/misc/escape.cc, src/misc/escape.hh (escape_rfc4180): New
function.
* src/bin/ltlcross.cc: Do not output space after ',', use
"\r\n" for end of line, and use escape_rfc4180().
* NEWS: Mention it.

src/misc/escape.cc

@@ -31,6 +31,22 @@
 
 namespace spot
 {
+  std::ostream&
+  escape_rfc4180(std::ostream& os, const std::string& str)
+  {
+    for (std::string::const_iterator i = str.begin(); i != str.end(); ++i)
+      switch (*i)
+	{
+	case '"':
+	  os << "\"\"";
+	  break;
+	default:
+	  os << *i;
+	  break;
+	}
+    return os;
+  }
+
   std::ostream&
   escape_str(std::ostream& os, const std::string& str)
   {