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/eval.c

@@ -12,12 +12,48 @@
  */
 
 #include "vim.h"
+#include "eval.h"
+#include "buffer.h"
+#include "charset.h"
+#include "diff.h"
+#include "edit.h"
+#include "ex_cmds.h"
+#include "ex_cmds2.h"
+#include "ex_docmd.h"
+#include "ex_eval.h"
+#include "ex_getln.h"
+#include "fileio.h"
+#include "fold.h"
+#include "getchar.h"
+#include "hashtab.h"
+#include "if_cscope.h"
+#include "mark.h"
+#include "mbyte.h"
+#include "memline.h"
+#include "message.h"
+#include "misc1.h"
+#include "misc2.h"
+#include "move.h"
+#include "normal.h"
+#include "ops.h"
+#include "option.h"
+#include "os_unix.h"
+#include "popupmnu.h"
+#include "quickfix.h"
+#include "regexp.h"
+#include "screen.h"
+#include "search.h"
+#include "sha256.h"
+#include "spell.h"
+#include "syntax.h"
+#include "tag.h"
+#include "term.h"
+#include "ui.h"
+#include "undo.h"
+#include "version.h"
+#include "window.h"
 #include "os/os.h"
 
-
-
-
-
 #if defined(FEAT_FLOAT) && defined(HAVE_MATH_H)
 # include <math.h>
 #endif
@@ -264,7 +300,7 @@ typedef struct {
  * The reason to use this table anyway is for very quick access to the
  * variables with the VV_ defines.
  */
-#include "version.h"
+#include "version_defs.h"
 
 /* values for vv_flags: */
 #define VV_COMPAT       1       /* compatible, also used without "v:" */