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/normal.h

@@ -56,31 +56,8 @@ typedef struct cmdarg_S {
 #define CA_COMMAND_BUSY     1   /* skip restarting edit() once */
 #define CA_NO_ADJ_OP_END    2   /* don't adjust operator end */
 
-void init_normal_cmds(void);
-void normal_cmd(oparg_T *oap, int toplevel);
-void do_pending_operator(cmdarg_T *cap, int old_col, int gui_yank);
-int do_mouse(oparg_T *oap, int c, int dir, long count, int fixindent);
-void check_visual_highlight(void);
-void end_visual_mode(void);
-void reset_VIsual_and_resel(void);
-void reset_VIsual(void);
-int find_ident_under_cursor(char_u **string, int find_type);
-int find_ident_at_pos(win_T *wp, linenr_T lnum, colnr_T startcol,
-                      char_u **string,
-                      int find_type);
-void clear_showcmd(void);
-int add_to_showcmd(int c);
-void add_to_showcmd_c(int c);
-void push_showcmd(void);
-void pop_showcmd(void);
-void do_check_scrollbind(int check);
-void check_scrollbind(linenr_T topline_diff, long leftcol_diff);
-int find_decl(char_u *ptr, int len, int locally, int thisblock,
-              int searchflags);
-void scroll_redraw(int up, long count);
-void do_nv_ident(int c1, int c2);
-int get_visual_text(cmdarg_T *cap, char_u **pp, int *lenp);
-void start_selection(void);
-void may_start_select(int c);
 
+#ifdef INCLUDE_GENERATED_DECLARATIONS
+# include "normal.h.generated.h"
+#endif
 #endif /* NVIM_NORMAL_H */