Refactor modules in Python bindings. Start work on grammar-update functions, but without transactions.

src/runtime/python/ffi.h

@@ -0,0 +1,24 @@
+#ifndef PYPGF_MARSHALLER_H_
+#define PYPGF_MARSHALLER_H_
+
+#define PY_SSIZE_T_CLEAN
+#include <Python.h>
+
+#include <pgf/pgf.h>
+
+typedef struct {
+    PyObject_HEAD
+    PgfDB *db;
+    PgfRevision revision;
+} PGFObject;
+
+extern PyObject *PGFError;
+PgfExnType handleError(PgfExn err);
+
+PgfText *PyUnicode_AsPgfText(PyObject *pystr);
+PyObject *PyUnicode_FromPgfText(PgfText *text);
+
+extern PgfUnmarshaller unmarshaller;
+extern PgfMarshaller marshaller;
+
+#endif // PYPGF_MARSHALLER_H_