Removes 'proto' dir

See #137 for the issue.

Every header in the proto directory was:

* Given include guards in the form

    #ifndef NEOVIM_FILENAME_H
    #define NEOVIM_FILENAME_H
        ...
    #endif /* NEOVIM_FILENAM_H */

* Renamed from *.pro -> *.h
* Moved from src/proto/ to src/

This would have caused conficts with some existing headers in src/;
rather than merge these conflicts now (which is a whole other can of
worms involving multiple and conditional inclusion), any header in src/
with a conflicting name was renamed from *.h -> *_defs.h (which may or
may not actually describe its purpose, the change is purely a
namespacing issue).

Once all of these changes were made a script was developed to determine
what #includes needed to be added to each source file to describe its
dependencies and allow it to compile; because the script is so short
and I'll just list it here:

    #! /bin/bash

    cd $(dirname $0)

    # Scrapes `make` output for provided error messages and outputs #includes
    # needed to resolve them.
    #   $1 : part of the clang error message between filename and identifier
    list_missing_includes() {
        for file_missing_pair in $(CC=clang make 2>&1 >/dev/null | sed -n "s/\/\(.*\.[hc]\).*$1.*'\(.*\)'.*/\1:\2/p"); do
            fields=(${file_missing_pair//:/ })
            source_file=${fields[0]}
            missing_func=${fields[1]}
            # Try to find the declaration of the missing function.
            echo $(basename $source_file) \
                \#include \"$(grep -r "\b$missing_func __ARGS" | sed -n "s/.*\/\(.*\)\:.*/\1/p")\"
        # Remove duplicates
        done | sort | uniq
    }

    echo "Finding missing function prototypes..."
    list_missing_includes "implicit declaration of function"
    echo "Finding missing identifier declarations..."
    list_missing_includes "use of undeclared identifier"

Each list of required headers was added by hand in the following format:

    #include "vim.h"
    #include "*_defs.h"
    #include "filename.h"
    /* All other includes in same module here, in alphabetical order. */
    /* All includes from other modules (e.g. "os/*.h") here in alphabetical
     * order. */

src/syntax.h

@@ -0,0 +1,61 @@
+#ifndef NEOVIM_SYNTAX_H
+#define NEOVIM_SYNTAX_H
+/* syntax.c */
+void syntax_start __ARGS((win_T *wp, linenr_T lnum));
+void syn_stack_free_all __ARGS((synblock_T *block));
+void syn_stack_apply_changes __ARGS((buf_T *buf));
+void syntax_end_parsing __ARGS((linenr_T lnum));
+int syntax_check_changed __ARGS((linenr_T lnum));
+int get_syntax_attr __ARGS((colnr_T col, int *can_spell, int keep_state));
+void syntax_clear __ARGS((synblock_T *block));
+void reset_synblock __ARGS((win_T *wp));
+void ex_syntax __ARGS((exarg_T *eap));
+void ex_ownsyntax __ARGS((exarg_T *eap));
+int syntax_present __ARGS((win_T *win));
+void reset_expand_highlight __ARGS((void));
+void set_context_in_echohl_cmd __ARGS((expand_T *xp, char_u *arg));
+void set_context_in_syntax_cmd __ARGS((expand_T *xp, char_u *arg));
+char_u *get_syntax_name __ARGS((expand_T *xp, int idx));
+int syn_get_id __ARGS((win_T *wp, long lnum, colnr_T col, int trans,
+                       int *spellp,
+                       int keep_state));
+int get_syntax_info __ARGS((int *seqnrp));
+int syn_get_sub_char __ARGS((void));
+int syn_get_stack_item __ARGS((int i));
+int syn_get_foldlevel __ARGS((win_T *wp, long lnum));
+void ex_syntime __ARGS((exarg_T *eap));
+char_u *get_syntime_arg __ARGS((expand_T *xp, int idx));
+void init_highlight __ARGS((int both, int reset));
+int load_colors __ARGS((char_u *name));
+void do_highlight __ARGS((char_u *line, int forceit, int init));
+void free_highlight __ARGS((void));
+void restore_cterm_colors __ARGS((void));
+void set_normal_colors __ARGS((void));
+char_u *hl_get_font_name __ARGS((void));
+void hl_set_font_name __ARGS((char_u *font_name));
+void hl_set_bg_color_name __ARGS((char_u *name));
+void hl_set_fg_color_name __ARGS((char_u *name));
+void clear_hl_tables __ARGS((void));
+int hl_combine_attr __ARGS((int char_attr, int prim_attr));
+attrentry_T *syn_gui_attr2entry __ARGS((int attr));
+int syn_attr2attr __ARGS((int attr));
+attrentry_T *syn_term_attr2entry __ARGS((int attr));
+attrentry_T *syn_cterm_attr2entry __ARGS((int attr));
+char_u *highlight_has_attr __ARGS((int id, int flag, int modec));
+char_u *highlight_color __ARGS((int id, char_u *what, int modec));
+long_u highlight_gui_color_rgb __ARGS((int id, int fg));
+int syn_name2id __ARGS((char_u *name));
+int highlight_exists __ARGS((char_u *name));
+char_u *syn_id2name __ARGS((int id));
+int syn_namen2id __ARGS((char_u *linep, int len));
+int syn_check_group __ARGS((char_u *pp, int len));
+int syn_id2attr __ARGS((int hl_id));
+int syn_id2colors __ARGS((int hl_id, guicolor_T *fgp, guicolor_T *bgp));
+int syn_get_final_id __ARGS((int hl_id));
+void highlight_gui_started __ARGS((void));
+int highlight_changed __ARGS((void));
+void set_context_in_highlight_cmd __ARGS((expand_T *xp, char_u *arg));
+char_u *get_highlight_name __ARGS((expand_T *xp, int idx));
+void free_highlight_fonts __ARGS((void));
+/* vim: set ft=c : */
+#endif /* NEOVIM_SYNTAX_H */