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/option.c

@@ -11,7 +11,7 @@
  * Code to handle user-settable options. This is all pretty much table-
  * driven. Checklist for adding a new option:
  * - Put it in the options array below (copy an existing entry).
- * - For a global option: Add a variable for it in option.h.
+ * - For a global option: Add a variable for it in option_defs.h.
  * - For a buffer or window local option:
  *   - Add a PV_XX entry to the enum below.
  *   - Add a variable to the window or buffer struct in structs.h.
@@ -33,6 +33,37 @@
 
 #define IN_OPTION_C
 #include "vim.h"
+#include "option.h"
+#include "blowfish.h"
+#include "buffer.h"
+#include "charset.h"
+#include "diff.h"
+#include "digraph.h"
+#include "eval.h"
+#include "ex_cmds2.h"
+#include "ex_docmd.h"
+#include "ex_getln.h"
+#include "fileio.h"
+#include "fold.h"
+#include "getchar.h"
+#include "hardcopy.h"
+#include "mbyte.h"
+#include "memfile.h"
+#include "memline.h"
+#include "message.h"
+#include "misc1.h"
+#include "misc2.h"
+#include "move.h"
+#include "normal.h"
+#include "os_unix.h"
+#include "regexp.h"
+#include "screen.h"
+#include "spell.h"
+#include "syntax.h"
+#include "term.h"
+#include "ui.h"
+#include "undo.h"
+#include "window.h"
 
 /*
  * The options that are local to a window or buffer have "indir" set to one of
@@ -52,7 +83,7 @@
 
 /*
  * Definition of the PV_ values for buffer-local options.
- * The BV_ values are defined in option.h.
+ * The BV_ values are defined in option_defs.h.
  */
 #define PV_AI           OPT_BUF(BV_AI)
 #define PV_AR           OPT_BOTH(OPT_BUF(BV_AR))
@@ -130,7 +161,7 @@
 
 /*
  * Definition of the PV_ values for window-local options.
- * The WV_ values are defined in option.h.
+ * The WV_ values are defined in option_defs.h.
  */
 #define PV_LIST         OPT_WIN(WV_LIST)
 # define PV_ARAB        OPT_WIN(WV_ARAB)