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/if_cscope.h

@@ -0,0 +1,16 @@
+#ifndef NEOVIM_IF_CSCOPE_H
+#define NEOVIM_IF_CSCOPE_H
+/* if_cscope.c */
+char_u *get_cscope_name(expand_T *xp, int idx);
+void set_context_in_cscope_cmd(expand_T *xp, char_u *arg,
+                               cmdidx_T cmdidx);
+void do_cscope(exarg_T *eap);
+void do_scscope(exarg_T *eap);
+void do_cstag(exarg_T *eap);
+int cs_fgets(char_u *buf, int size);
+void cs_free_tags(void);
+void cs_print_tags(void);
+int cs_connection(int num, char_u *dbpath, char_u *ppath);
+void cs_end(void);
+
+#endif /* NEOVIM_IF_CSCOPE_H */