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/vim.h

@@ -6,8 +6,8 @@
  * Do ":help credits" in Vim to see a list of people who contributed.
  */
 
-#ifndef VIM__H
-# define VIM__H
+#ifndef NEOVIM_VIM_H
+# define NEOVIM_VIM_H
 /* Included when ported to cmake */
 /* This is needed to replace TRUE/FALSE macros by true/false from c99 */
 #include <stdbool.h>
@@ -62,7 +62,7 @@ Error: configure did not run properly.Check auto/config.log.
 # define VIMPACKAGE     "vim"
 #endif
 
-#include "os_unix.h"       /* bring lots of system header files */
+#include "os_unix_defs.h"       /* bring lots of system header files */
 
 #ifndef __ARGS
 # if defined(__STDC__) || defined(__GNUC__) || defined(WIN3264)
@@ -154,7 +154,7 @@ typedef unsigned long u8char_T;     /* long should be 32 bits or more */
 
 #include "ascii.h"
 #include "keymap.h"
-#include "term.h"
+#include "term_defs.h"
 #include "macros.h"
 
 #include <errno.h>
@@ -1260,9 +1260,9 @@ int vim_memcmp __ARGS((void *, void *, size_t));
 
 typedef struct timeval proftime_T;
 
-/* Include option.h before structs.h, because the number of window-local and
+/* Include option_defs.h before structs.h, because the number of window-local and
  * buffer-local options is used there. */
-#include "option.h"         /* options and default values */
+#include "option_defs.h"         /* options and default values */
 
 /* Note that gui.h is included by structs.h */
 
@@ -1412,7 +1412,7 @@ typedef struct timeval proftime_T;
 typedef int VimClipboard;       /* This is required for the prototypes. */
 
 
-#include "ex_cmds.h"        /* Ex command defines */
+#include "ex_cmds_defs.h"        /* Ex command defines */
 #include "proto.h"          /* function prototypes */
 
 /* This has to go after the include of proto.h, as proto/gui.pro declares
@@ -1594,4 +1594,4 @@ typedef int VimClipboard;       /* This is required for the prototypes. */
 # define SET_NO_HLSEARCH(flag) no_hlsearch = (flag); set_vim_var_nr( \
     VV_HLSEARCH, !no_hlsearch)
 
-#endif /* VIM__H */
+#endif /* NEOVIM_VIM_H */