Refactor API types and prototypes

- Split functions with multiple files in the 'api' subdirectory
- Move/Add more types in the 'api/defs.h' header
- Add more prototypes
- Refactor scripts/msgpack-gen.lua
- Move msgpack modules to 'os' subdirectory

src/api/window.c

@@ -0,0 +1,73 @@
+#include <stdbool.h>
+#include <stdint.h>
+#include <stdlib.h>
+
+#include "api/window.h"
+#include "api/defs.h"
+
+
+Buffer window_get_buffer(Window window, Error *err)
+{
+  abort();
+}
+
+Position window_get_cursor(Window window, Error *err)
+{
+  abort();
+}
+
+void window_set_cursor(Window window, Position pos, Error *err)
+{
+  abort();
+}
+
+int64_t window_get_height(Window window, Error *err)
+{
+  abort();
+}
+
+void window_set_height(Window window, int64_t height, Error *err)
+{
+  abort();
+}
+
+int64_t window_get_width(Window window, Error *err)
+{
+  abort();
+}
+
+Object window_get_var(Window window, String name, Error *err)
+{
+  abort();
+}
+
+void window_set_var(Window window, String name, Object value, Error *err)
+{
+  abort();
+}
+
+String window_get_option(Window window, String name, Error *err)
+{
+  abort();
+}
+
+void window_set_option(Window window, String name, String value, Error *err)
+{
+  abort();
+}
+
+Position window_get_pos(Window window, Error *err)
+{
+  abort();
+}
+
+Tabpage window_get_tabpage(Window window, Error *err)
+{
+  abort();
+}
+
+bool window_is_valid(Window window)
+{
+  abort();
+}
+