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/file_search.h

@@ -0,0 +1,23 @@
+#ifndef NEOVIM_FILE_SEARCH_H
+#define NEOVIM_FILE_SEARCH_H
+
+void *vim_findfile_init(char_u *path, char_u *filename, char_u *
+                                stopdirs, int level, int free_visited,
+                                int find_what, void *search_ctx_arg,
+                                int tagfile,
+                                char_u *rel_fname);
+char_u *vim_findfile_stopdir(char_u *buf);
+void vim_findfile_cleanup(void *ctx);
+char_u *vim_findfile(void *search_ctx_arg);
+void vim_findfile_free_visited(void *search_ctx_arg);
+char_u *find_file_in_path(char_u *ptr, int len, int options, int first,
+                                  char_u *rel_fname);
+void free_findfile(void);
+char_u *find_directory_in_path(char_u *ptr, int len, int options,
+                                       char_u *rel_fname);
+char_u *find_file_in_path_option(char_u *ptr, int len, int options,
+                                         int first, char_u *path_option,
+                                         int find_what, char_u *rel_fname,
+                                         char_u *suffixes);
+
+#endif /* NEOVIM_FILE_SEARCH_H */