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/misc1.h

@@ -3,72 +3,7 @@
 
 #include "nvim/vim.h"
 
-int open_line(int dir, int flags, int second_line_indent);
-int get_leader_len(char_u *line, char_u **flags, int backward,
-                   int include_space);
-int get_last_leader_offset(char_u *line, char_u **flags);
-int plines(linenr_T lnum);
-int plines_win(win_T *wp, linenr_T lnum, int winheight);
-int plines_nofill(linenr_T lnum);
-int plines_win_nofill(win_T *wp, linenr_T lnum, int winheight);
-int plines_win_nofold(win_T *wp, linenr_T lnum);
-int plines_win_col(win_T *wp, linenr_T lnum, long column);
-int plines_m_win(win_T *wp, linenr_T first, linenr_T last);
-void ins_bytes(char_u *p);
-void ins_bytes_len(char_u *p, int len);
-void ins_char(int c);
-void ins_char_bytes(char_u *buf, int charlen);
-void ins_str(char_u *s);
-int del_char(int fixpos);
-int del_chars(long count, int fixpos);
-int del_bytes(long count, int fixpos_arg, int use_delcombine);
-void truncate_line(int fixpos);
-void del_lines(long nlines, int undo);
-int gchar_pos(pos_T *pos);
-char_u *skip_to_option_part(char_u *p);
-void changed(void);
-void changed_int(void);
-void changed_bytes(linenr_T lnum, colnr_T col);
-void appended_lines(linenr_T lnum, long count);
-void appended_lines_mark(linenr_T lnum, long count);
-void deleted_lines(linenr_T lnum, long count);
-void deleted_lines_mark(linenr_T lnum, long count);
-void changed_lines(linenr_T lnum, colnr_T col, linenr_T lnume,
-                   long xtra);
-void unchanged(buf_T *buf, int ff);
-void check_status(buf_T *buf);
-void change_warning(int col);
-int ask_yesno(char_u *str, int direct);
-int is_mouse_key(int c);
-int get_keystroke(void);
-int get_number(int colon, int *mouse_used);
-int prompt_for_number(int *mouse_used);
-void msgmore(long n);
-void beep_flush(void);
-void vim_beep(void);
-void init_homedir(void);
-void free_homedir(void);
-void free_users(void);
-char_u *expand_env_save(char_u *src);
-char_u *expand_env_save_opt(char_u *src, int one);
-void expand_env(char_u *src, char_u *dst, int dstlen);
-void expand_env_esc(char_u *srcp, char_u *dst, int dstlen, int esc,
-                    int one,
-                    char_u *startstr);
-char_u *vim_getenv(char_u *name, int *mustfree);
-void vim_setenv(char_u *name, char_u *val);
-char_u *get_env_name(expand_T *xp, int idx);
-char_u *get_users(expand_T *xp, int idx);
-int match_user(char_u *name);
-void home_replace(buf_T *buf, char_u *src, char_u *dst, int dstlen,
-                  int one);
-char_u *home_replace_save(buf_T *buf, char_u *src);
-void prepare_to_exit(void);
-void preserve_exit(void);
-void line_breakcheck(void);
-void fast_breakcheck(void);
-char_u *get_cmd_output(char_u *cmd, char_u *infile, int flags);
-void FreeWild(int count, char_u **files);
-int goto_im(void);
-
-#endif /* NVIM_MISC1_H */
+#ifdef INCLUDE_GENERATED_DECLARATIONS
+# include "misc1.h.generated.h"
+#endif
+#endif  // NVIM_MISC1_H