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/edit.h

@@ -0,0 +1,49 @@
+#ifndef NEOVIM_EDIT_H
+#define NEOVIM_EDIT_H
+/* edit.c */
+int edit __ARGS((int cmdchar, int startln, long count));
+void edit_putchar __ARGS((int c, int highlight));
+void edit_unputchar __ARGS((void));
+void display_dollar __ARGS((colnr_T col));
+void change_indent __ARGS((int type, int amount, int round, int replaced,
+                           int call_changed_bytes));
+void truncate_spaces __ARGS((char_u *line));
+void backspace_until_column __ARGS((int col));
+int vim_is_ctrl_x_key __ARGS((int c));
+int ins_compl_add_infercase __ARGS((char_u *str, int len, int icase, char_u *
+                                    fname, int dir,
+                                    int flags));
+void set_completion __ARGS((colnr_T startcol, list_T *list));
+void ins_compl_show_pum __ARGS((void));
+char_u *find_word_start __ARGS((char_u *ptr));
+char_u *find_word_end __ARGS((char_u *ptr));
+int ins_compl_active __ARGS((void));
+int ins_compl_add_tv __ARGS((typval_T *tv, int dir));
+void ins_compl_check_keys __ARGS((int frequency));
+int get_literal __ARGS((void));
+void insertchar __ARGS((int c, int flags, int second_indent));
+void auto_format __ARGS((int trailblank, int prev_line));
+int comp_textwidth __ARGS((int ff));
+int stop_arrow __ARGS((void));
+void set_last_insert __ARGS((int c));
+void free_last_insert __ARGS((void));
+char_u *add_char2buf __ARGS((int c, char_u *s));
+void beginline __ARGS((int flags));
+int oneright __ARGS((void));
+int oneleft __ARGS((void));
+int cursor_up __ARGS((long n, int upd_topline));
+int cursor_down __ARGS((long n, int upd_topline));
+int stuff_inserted __ARGS((int c, long count, int no_esc));
+char_u *get_last_insert __ARGS((void));
+char_u *get_last_insert_save __ARGS((void));
+void replace_push __ARGS((int c));
+int replace_push_mb __ARGS((char_u *p));
+void fixthisline __ARGS((int (*get_the_indent)(void)));
+void fix_indent __ARGS((void));
+int in_cinkeys __ARGS((int keytyped, int when, int line_is_empty));
+int hkmap __ARGS((int c));
+void ins_scroll __ARGS((void));
+void ins_horscroll __ARGS((void));
+int ins_copychar __ARGS((linenr_T lnum));
+/* vim: set ft=c : */
+#endif /* NEOVIM_EDIT_H */