examples: consolidate includes into "common.h"

Consolidate all standard includes and defines into "common.h". This lets
us avoid having to handle platform-specific things in multiple places.

examples/common.h

@@ -12,10 +12,25 @@
  * <http://creativecommons.org/publicdomain/zero/1.0/>.
  */
 
+#include <sys/types.h>
+#include <sys/stat.h>
 #include <stdio.h>
 #include <string.h>
 #include <stdlib.h>
 #include <git2.h>
+#include <fcntl.h>
+
+#ifdef _WIN32
+# include <io.h>
+# include <Windows.h>
+# define open _open
+# define read _read
+# define close _close
+# define ssize_t int
+# define sleep(a) Sleep(a * 1000)
+#else
+# include <unistd.h>
+#endif
 
 #ifndef PRIuZ
 /* Define the printf format specifer to use for size_t output */

examples/for-each-ref.c

 #include <git2.h>
-#include <stdio.h>
 #include "common.h"
 
 static int show_ref(git_reference *ref, void *data)

examples/general.c

@@ -36,6 +36,8 @@
  * [pg]: https://git-scm.com/book/en/v2/Git-Internals-Plumbing-and-Porcelain
  */
 
+#include "common.h"
+
 /**
  * ### Includes
  *
@@ -43,9 +45,7 @@
  * that you need.  It should be the only thing you need to include in order
  * to compile properly and get all the libgit2 API.
  */
-#include <git2.h>
-#include <stdio.h>
-#include <string.h>
+#include "git2.h"
 
 static void oid_parsing(git_oid *out);
 static void object_database(git_repository *repo, git_oid *oid);

examples/index-pack.c

 #include "common.h"
 
-#include <sys/types.h>
-#include <sys/stat.h>
-#include <fcntl.h>
-#ifdef _WIN32
-# include <io.h>
-# include <Windows.h>
-
-# define open _open
-# define read _read
-# define close _close
-
-#define ssize_t int
-#else
-# include <unistd.h>
-#endif
-
 /*
  * This could be run in the main loop whilst the application waits for
  * the indexing to finish in a worker thread

examples/status.c

@@ -13,12 +13,6 @@
  */
 
 #include "common.h"
-#ifdef _WIN32
-# include <Windows.h>
-# define sleep(a) Sleep(a * 1000)
-#else
-# include <unistd.h>
-#endif
 
 /**
  * This example demonstrates the use of the libgit2 status APIs,