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/os_unix.h

@@ -0,0 +1,46 @@
+#ifndef NEOVIM_OS_UNIX_H
+#define NEOVIM_OS_UNIX_H
+
+#include "os/shell.h"
+
+/* os_unix.c */
+void mch_write(char_u *s, int len);
+void mch_suspend(void);
+void mch_init(void);
+int mch_can_restore_title(void);
+int mch_can_restore_icon(void);
+void mch_settitle(char_u *title, char_u *icon);
+void mch_restore_title(int which);
+int vim_is_xterm(char_u *name);
+int use_xterm_like_mouse(char_u *name);
+int use_xterm_mouse(void);
+int vim_is_iris(char_u *name);
+int vim_is_vt300(char_u *name);
+int vim_is_fastterm(char_u *name);
+void slash_adjust(char_u *p);
+void fname_case(char_u *name, int len);
+void mch_copy_sec(char_u *from_file, char_u *to_file);
+vim_acl_T mch_get_acl(char_u *fname);
+void mch_set_acl(char_u *fname, vim_acl_T aclent);
+void mch_free_acl(vim_acl_T aclent);
+void mch_hide(char_u *name);
+int mch_nodetype(char_u *name);
+void mch_early_init(void);
+void mch_free_mem(void);
+void mch_exit(int r);
+void mch_settmode(int tmode);
+void get_stty(void);
+void mch_setmouse(int on);
+void check_mouse_termcode(void);
+int mch_get_shellsize(void);
+void mch_set_shellsize(void);
+int mch_expand_wildcards(int num_pat, char_u **pat, int *num_file,
+                         char_u ***file,
+                         int flags);
+int mch_has_exp_wildcard(char_u *p);
+int mch_has_wildcard(char_u *p);
+int mch_libcall(char_u *libname, char_u *funcname, char_u *argstring,
+                int argint, char_u **string_result,
+                int *number_result);
+
+#endif /* NEOVIM_OS_UNIX_H */