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/message.h

@@ -0,0 +1,83 @@
+#ifndef NEOVIM_MESSAGE_H
+#define NEOVIM_MESSAGE_H
+/* message.c */
+int msg __ARGS((char_u *s));
+int verb_msg __ARGS((char_u *s));
+int msg_attr __ARGS((char_u *s, int attr));
+int msg_attr_keep __ARGS((char_u *s, int attr, int keep));
+char_u *msg_strtrunc __ARGS((char_u *s, int force));
+void trunc_string __ARGS((char_u *s, char_u *buf, int room, int buflen));
+void reset_last_sourcing __ARGS((void));
+void msg_source __ARGS((int attr));
+int emsg_not_now __ARGS((void));
+int emsg __ARGS((char_u *s));
+int emsg2 __ARGS((char_u *s, char_u *a1));
+void emsg_invreg __ARGS((int name));
+char_u *msg_trunc_attr __ARGS((char_u *s, int force, int attr));
+char_u *msg_may_trunc __ARGS((int force, char_u *s));
+int delete_first_msg __ARGS((void));
+void ex_messages __ARGS((exarg_T *eap));
+void msg_end_prompt __ARGS((void));
+void wait_return __ARGS((int redraw));
+void set_keep_msg __ARGS((char_u *s, int attr));
+void set_keep_msg_from_hist __ARGS((void));
+void msg_start __ARGS((void));
+void msg_starthere __ARGS((void));
+void msg_putchar __ARGS((int c));
+void msg_putchar_attr __ARGS((int c, int attr));
+void msg_outnum __ARGS((long n));
+void msg_home_replace __ARGS((char_u *fname));
+void msg_home_replace_hl __ARGS((char_u *fname));
+int msg_outtrans __ARGS((char_u *str));
+int msg_outtrans_attr __ARGS((char_u *str, int attr));
+int msg_outtrans_len __ARGS((char_u *str, int len));
+char_u *msg_outtrans_one __ARGS((char_u *p, int attr));
+int msg_outtrans_len_attr __ARGS((char_u *msgstr, int len, int attr));
+void msg_make __ARGS((char_u *arg));
+int msg_outtrans_special __ARGS((char_u *strstart, int from));
+char_u *str2special_save __ARGS((char_u *str, int is_lhs));
+char_u *str2special __ARGS((char_u **sp, int from));
+void str2specialbuf __ARGS((char_u *sp, char_u *buf, int len));
+void msg_prt_line __ARGS((char_u *s, int list));
+void msg_puts __ARGS((char_u *s));
+void msg_puts_title __ARGS((char_u *s));
+void msg_puts_long_attr __ARGS((char_u *longstr, int attr));
+void msg_puts_long_len_attr __ARGS((char_u *longstr, int len, int attr));
+void msg_puts_attr __ARGS((char_u *s, int attr));
+void may_clear_sb_text __ARGS((void));
+void clear_sb_text __ARGS((void));
+void show_sb_text __ARGS((void));
+void msg_sb_eol __ARGS((void));
+int msg_use_printf __ARGS((void));
+void mch_errmsg __ARGS((char *str));
+void mch_msg __ARGS((char *str));
+void msg_moremsg __ARGS((int full));
+void repeat_message __ARGS((void));
+void msg_clr_eos __ARGS((void));
+void msg_clr_eos_force __ARGS((void));
+void msg_clr_cmdline __ARGS((void));
+int msg_end __ARGS((void));
+void msg_check __ARGS((void));
+int redirecting __ARGS((void));
+void verbose_enter __ARGS((void));
+void verbose_leave __ARGS((void));
+void verbose_enter_scroll __ARGS((void));
+void verbose_leave_scroll __ARGS((void));
+void verbose_stop __ARGS((void));
+int verbose_open __ARGS((void));
+void give_warning __ARGS((char_u *message, int hl));
+void msg_advance __ARGS((int col));
+int do_dialog __ARGS((int type, char_u *title, char_u *message, char_u *buttons,
+                      int dfltbutton, char_u *textfield,
+                      int ex_cmd));
+void display_confirm_msg __ARGS((void));
+int vim_dialog_yesno __ARGS((int type, char_u *title, char_u *message, int dflt));
+int vim_dialog_yesnocancel __ARGS((int type, char_u *title, char_u *message,
+                                   int dflt));
+int vim_dialog_yesnoallcancel __ARGS((int type, char_u *title, char_u *message,
+                                      int dflt));
+char_u *do_browse __ARGS((int flags, char_u *title, char_u *dflt, char_u *ext,
+                          char_u *initdir, char_u *filter,
+                          buf_T *buf));
+/* vim: set ft=c : */
+#endif /* NEOVIM_MESSAGE_H */