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/undo.h

@@ -0,0 +1,36 @@
+#ifndef NEOVIM_UNDO_H
+#define NEOVIM_UNDO_H
+
+#include "undo_defs.h"
+
+/* undo.c */
+int u_save_cursor(void);
+int u_save(linenr_T top, linenr_T bot);
+int u_savesub(linenr_T lnum);
+int u_inssub(linenr_T lnum);
+int u_savedel(linenr_T lnum, long nlines);
+int undo_allowed(void);
+int u_savecommon(linenr_T top, linenr_T bot, linenr_T newbot,
+                 int reload);
+void u_compute_hash(char_u *hash);
+char_u *u_get_undo_file_name(char_u *buf_ffname, int reading);
+void u_write_undo(char_u *name, int forceit, buf_T *buf, char_u *hash);
+void u_read_undo(char_u *name, char_u *hash, char_u *orig_name);
+void u_undo(int count);
+void u_redo(int count);
+void undo_time(long step, int sec, int file, int absolute);
+void u_sync(int force);
+void ex_undolist(exarg_T *eap);
+void ex_undojoin(exarg_T *eap);
+void u_unchanged(buf_T *buf);
+void u_find_first_changed(void);
+void u_update_save_nr(buf_T *buf);
+void u_clearall(buf_T *buf);
+void u_saveline(linenr_T lnum);
+void u_clearline(void);
+void u_undoline(void);
+void u_blockfree(buf_T *buf);
+int bufIsChanged(buf_T *buf);
+int curbufIsChanged(void);
+void u_eval_tree(u_header_T *first_uhp, list_T *list);
+#endif /* NEOVIM_UNDO_H */