Introduce nvim namespace: Move files.

Move files from src/ to src/nvim/.
- src/nvim/ becomes the new root dir for nvim executable sources.
- src/libnvim/ is planned to become root dir of the neovim library.

src/nvim/garray.h

@@ -0,0 +1,31 @@
+#ifndef NEOVIM_GARRAY_H
+#define NEOVIM_GARRAY_H
+
+#include "func_attr.h"
+
+/// Structure used for growing arrays.
+/// This is used to store information that only grows, is deleted all at
+/// once, and needs to be accessed by index.  See ga_clear() and ga_grow().
+typedef struct growarray {
+  int ga_len;                       // current number of items used
+  int ga_maxlen;                    // maximum number of items possible
+  int ga_itemsize;                  // sizeof(item)
+  int ga_growsize;                  // number of items to grow each time
+  void *ga_data;                    // pointer to the first item
+} garray_T;
+
+#define GA_EMPTY { 0, 0, 0, 0, NULL }
+
+void ga_clear(garray_T *gap);
+void ga_clear_strings(garray_T *gap);
+void ga_init(garray_T *gap, int itemsize, int growsize);
+void ga_grow(garray_T *gap, int n);
+char_u *ga_concat_strings_sep(const garray_T *gap, const char *sep)
+  FUNC_ATTR_NONNULL_RET;
+char_u *ga_concat_strings(const garray_T *gap) FUNC_ATTR_NONNULL_RET;
+void ga_remove_duplicate_strings(garray_T *gap);
+void ga_concat(garray_T *gap, const char_u *restrict s);
+void ga_append(garray_T *gap, char c);
+void append_ga_line(garray_T *gap);
+
+#endif  // NEOVIM_GARRAY_H