ParsingScope to pass around parser rules.

Sort of a comeback of an old idea. It's either this,
or adding a third parameter soon for lexicons.
I went with this as this makes it easier to add yet
another thing to toss around, if such need ever arises.

libwccl/parser/parsingscope.h

+#ifndef LIBWCCL_PARSER_PARSINGSCOPE_H
+#define LIBWCCL_PARSER_PARSINGSCOPE_H
+
+#include <libwccl/variables.h>
+
+namespace Wccl {
+
+class ParsingScope
+{
+public:
+	ParsingScope(const Corpus2::Tagset& tagset)
+		: tagset_(tagset),
+		  variables_()
+	{
+	}
+
+	const Corpus2::Tagset& tagset() {
+		return tagset_;
+	}
+
+	Variables& variables() {
+		return variables_;
+	}
+
+private:
+	const Corpus2::Tagset& tagset_;
+	Variables variables_;
+};
+
+} /* end ns Wccl */
+
+#endif // LIBWCCL_PARSER_PARSINGSCOPE_H