Add peek buffer to io, hide file/buffer private functions

Implements peek buffer on top of the raw io read (with small storage
optimization). Hides implementation details of the file/buffer.

include/bh/file.h

@@ -8,36 +8,8 @@ typedef struct bh_file_s bh_file_t;
 
 bh_file_t *bh_file_new(const char *path);
 
-void bh_file_free(bh_file_t *file);
-
-int bh_file_open_base(bh_file_t *file,
-                      int mode);
-
-void bh_file_close_base(bh_file_t *file);
-
-int bh_file_is_open_base(bh_file_t *file);
-
-size_t bh_file_read_base(bh_file_t *file,
-                         char *data,
-                         size_t size);
-
-size_t bh_file_write_base(bh_file_t *file,
-                          const char *data,
-                          size_t size);
-
-void bh_file_flush_base(bh_file_t *file);
-
-int bh_file_seek_base(bh_file_t *file,
-                      bh_off_t pos,
-                      int dir);
-
-bh_off_t bh_file_size_base(bh_file_t *file);
-
-bh_off_t bh_file_tell_base(bh_file_t *file);
-
-bh_off_t bh_file_available_base(bh_file_t *file);
-
-void bh_file_clear_base(bh_file_t *file);
+#define bh_file_free(file) \
+    bh_io_free((bh_io_t *)(file))
 
 #define bh_file_open(file, mode) \
     bh_io_open((bh_io_t *)(file), (mode))
@@ -51,6 +23,9 @@ void bh_file_clear_base(bh_file_t *file);
 #define bh_file_read(file, data, size) \
     bh_io_read((bh_io_t *)(file), (data), (size))
 
+#define bh_file_peek(file, data, size) \
+    bh_io_peek((bh_io_t *)(file), (data), (size))
+
 #define bh_file_write(file, data, size) \
     bh_io_write((bh_io_t *)(file), (data), (size))