Add simple type for describing boundary conditions for the flow

equation.

flow_bc.h

@@ -0,0 +1,20 @@
+#ifndef FLOW_BC_H_INCLUDED
+#define FLOW_BC_H_INCLUDED
+
+#include <stddef.h>
+
+enum flowbc_type { UNSET, PRESSURE, FLUX };
+
+typedef struct {
+    enum flowbc_type *type;
+    double           *bcval;
+} flowbc_t;
+
+
+flowbc_t *
+allocate_flowbc(size_t nf);
+
+void
+deallocate_flowbc(flowbc_t *fbc);
+
+#endif  /* FLOW_BC_H_INCLUDED */