Refactor the code into separate files

Separate repository/odb functions into their own file. Add odb_exists
to go through the repository's odb. Adjust the test script.

c_src/repository.h

@@ -0,0 +1,29 @@
+#ifndef GEEF_REPOSTIORY_H
+#define GEEF_REPOSTIORY_H
+
+#include "erl_nif.h"
+#include <git2.h>
+
+#define MAXBUFLEN       1024
+
+ERL_NIF_TERM geef_repository_open(ErlNifEnv *env, int argc, const ERL_NIF_TERM argv[]);
+ERL_NIF_TERM geef_repository_path(ErlNifEnv *env, int argc, const ERL_NIF_TERM argv[]);
+ERL_NIF_TERM geef_repository_odb(ErlNifEnv *env, int argc, const ERL_NIF_TERM argv[]);
+ERL_NIF_TERM geef_odb_exists(ErlNifEnv *env, int argc, const ERL_NIF_TERM argv[]);
+
+
+void geef_repository_free(ErlNifEnv *env, void *cd);
+void geef_odb_free(ErlNifEnv *env, void *cd);
+
+extern ErlNifResourceType *geef_repository_type;
+extern ErlNifResourceType *geef_odb_type;
+
+typedef struct {
+    git_repository *repo;
+} geef_repository;
+
+typedef struct {
+    git_odb *odb;
+} geef_odb;
+
+#endif