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/syntax.h

@@ -6,53 +6,8 @@
 typedef int guicolor_T;
 
 /* syntax.c */
-void syntax_start(win_T *wp, linenr_T lnum);
-void syn_stack_free_all(synblock_T *block);
-void syn_stack_apply_changes(buf_T *buf);
-void syntax_end_parsing(linenr_T lnum);
-int syntax_check_changed(linenr_T lnum);
-int get_syntax_attr(colnr_T col, int *can_spell, int keep_state);
-void syntax_clear(synblock_T *block);
-void reset_synblock(win_T *wp);
-void ex_syntax(exarg_T *eap);
-void ex_ownsyntax(exarg_T *eap);
-int syntax_present(win_T *win);
-void reset_expand_highlight(void);
-void set_context_in_echohl_cmd(expand_T *xp, char_u *arg);
-void set_context_in_syntax_cmd(expand_T *xp, char_u *arg);
-char_u *get_syntax_name(expand_T *xp, int idx);
-int syn_get_id(win_T *wp, long lnum, colnr_T col, int trans,
-               int *spellp,
-               int keep_state);
-int get_syntax_info(int *seqnrp);
-int syn_get_sub_char(void);
-int syn_get_stack_item(int i);
-int syn_get_foldlevel(win_T *wp, long lnum);
-void ex_syntime(exarg_T *eap);
-char_u *get_syntime_arg(expand_T *xp, int idx);
-void init_highlight(int both, int reset);
-int load_colors(char_u *name);
-void do_highlight(char_u *line, int forceit, int init);
-void free_highlight(void);
-void restore_cterm_colors(void);
-char_u *hl_get_font_name(void);
-void clear_hl_tables(void);
-int hl_combine_attr(int char_attr, int prim_attr);
-attrentry_T *syn_gui_attr2entry(int attr);
-int syn_attr2attr(int attr);
-attrentry_T *syn_term_attr2entry(int attr);
-attrentry_T *syn_cterm_attr2entry(int attr);
-char_u *highlight_has_attr(int id, int flag, int modec);
-char_u *highlight_color(int id, char_u *what, int modec);
-int syn_name2id(char_u *name);
-int highlight_exists(char_u *name);
-char_u *syn_id2name(int id);
-int syn_namen2id(char_u *linep, int len);
-int syn_check_group(char_u *pp, int len);
-int syn_id2attr(int hl_id);
-int syn_get_final_id(int hl_id);
-int highlight_changed(void);
-void set_context_in_highlight_cmd(expand_T *xp, char_u *arg);
-char_u *get_highlight_name(expand_T *xp, int idx);
+#ifdef INCLUDE_GENERATED_DECLARATIONS
+# include "syntax.h.generated.h"
+#endif
 
 #endif /* NVIM_SYNTAX_H */