Add automatic generation of headers

- The 'stripdecls.py' script replaces declarations in all headers by includes to
  generated headers.
  `ag '#\s*if(?!ndef NEOVIM_).*((?!#\s*endif).*\n)*#ifdef INCLUDE_GENERATED'`
  was used for this.
- Add and integrate gendeclarations.lua into the build system to generate the
  required includes.
- Add -Wno-unused-function
- Made a bunch of old-style definitions ANSI

This adds a requirement: all type and structure definitions must be present
before INCLUDE_GENERATED_DECLARATIONS-protected include.

Warning: mch_expandpath (path.h.generated.h) was moved manually. So far it is
the only exception.

src/nvim/screen.h

@@ -1,68 +1,8 @@
 #ifndef NVIM_SCREEN_H
 #define NVIM_SCREEN_H
 /* screen.c */
-void redraw_later(int type);
-void redraw_win_later(win_T *wp, int type);
-void redraw_later_clear(void);
-void redraw_all_later(int type);
-void redraw_curbuf_later(int type);
-void redraw_buf_later(buf_T *buf, int type);
-int redraw_asap(int type);
-void redrawWinline(linenr_T lnum, int invalid);
-void update_curbuf(int type);
-void update_screen(int type);
-int conceal_cursor_line(win_T *wp);
-void conceal_check_cursur_line(void);
-void update_single_line(win_T *wp, linenr_T lnum);
-void update_debug_sign(buf_T *buf, linenr_T lnum);
-void rl_mirror(char_u *str);
-void status_redraw_all(void);
-void status_redraw_curbuf(void);
-void redraw_statuslines(void);
-void win_redraw_last_status(frame_T *frp);
-void win_redr_status_matches(expand_T *xp, int num_matches, char_u *
-                             *matches, int match,
-                             int showtail);
-void win_redr_status(win_T *wp);
-int stl_connected(win_T *wp);
-int get_keymap_str(win_T *wp, char_u *buf, int len);
-void screen_putchar(int c, int row, int col, int attr);
-void screen_getbytes(int row, int col, char_u *bytes, int *attrp);
-void screen_puts(char_u *text, int row, int col, int attr);
-void screen_puts_len(char_u *text, int len, int row, int col, int attr);
-void screen_stop_highlight(void);
-void reset_cterm_colors(void);
-void screen_draw_rectangle(int row, int col, int height, int width,
-                           int invert);
-void screen_fill(int start_row, int end_row, int start_col, int end_col,
-                 int c1, int c2,
-                 int attr);
-void check_for_delay(int check_msg_scroll);
-int screen_valid(int doclear);
-void screenalloc(int doclear);
-void free_screenlines(void);
-void screenclear(void);
-int can_clear(char_u *p);
-void screen_start(void);
-void windgoto(int row, int col);
-void setcursor(void);
-int win_ins_lines(win_T *wp, int row, int line_count, int invalid,
-                  int mayclear);
-int win_del_lines(win_T *wp, int row, int line_count, int invalid,
-                  int mayclear);
-int screen_ins_lines(int off, int row, int line_count, int end,
-                     win_T *wp);
-int screen_del_lines(int off, int row, int line_count, int end,
-                     int force,
-                     win_T *wp);
-int showmode(void);
-void unshowmode(int force);
-void get_trans_bufname(buf_T *buf);
-int redrawing(void);
-int messaging(void);
-void showruler(int always);
-int number_width(win_T *wp);
-int screen_screencol(void);
-int screen_screenrow(void);
 
+#ifdef INCLUDE_GENERATED_DECLARATIONS
+# include "screen.h.generated.h"
+#endif
 #endif /* NVIM_SCREEN_H */