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/ex_docmd.h

@@ -0,0 +1,72 @@
+#ifndef NEOVIM_EX_DOCMD_H
+#define NEOVIM_EX_DOCMD_H
+/* ex_docmd.c */
+void do_exmode __ARGS((int improved));
+int do_cmdline_cmd __ARGS((char_u *cmd));
+int do_cmdline __ARGS((char_u *cmdline, char_u *
+                       (*fgetline)(int, void *, int), void *cookie,
+                       int flags));
+int getline_equal __ARGS((char_u *
+                          (*fgetline)(int, void *,
+                                      int), void *cookie, char_u *
+                          (*func)(int, void *,
+                                  int)));
+void *getline_cookie __ARGS((char_u *(*fgetline)(int, void *, int),
+                             void *cookie));
+int checkforcmd __ARGS((char_u **pp, char *cmd, int len));
+int modifier_len __ARGS((char_u *cmd));
+int cmd_exists __ARGS((char_u *name));
+char_u *set_one_cmd_context __ARGS((expand_T *xp, char_u *buff));
+char_u *skip_range __ARGS((char_u *cmd, int *ctx));
+void ex_ni __ARGS((exarg_T *eap));
+int expand_filename __ARGS((exarg_T *eap, char_u **cmdlinep, char_u **errormsgp));
+void separate_nextcmd __ARGS((exarg_T *eap));
+int ends_excmd __ARGS((int c));
+char_u *find_nextcmd __ARGS((char_u *p));
+char_u *check_nextcmd __ARGS((char_u *p));
+char_u *get_command_name __ARGS((expand_T *xp, int idx));
+void ex_comclear __ARGS((exarg_T *eap));
+void uc_clear __ARGS((garray_T *gap));
+char_u *get_user_commands __ARGS((expand_T *xp, int idx));
+char_u *get_user_cmd_flags __ARGS((expand_T *xp, int idx));
+char_u *get_user_cmd_nargs __ARGS((expand_T *xp, int idx));
+char_u *get_user_cmd_complete __ARGS((expand_T *xp, int idx));
+int parse_compl_arg __ARGS((char_u *value, int vallen, int *complp, long *argt,
+                            char_u **compl_arg));
+void not_exiting __ARGS((void));
+void tabpage_close __ARGS((int forceit));
+void tabpage_close_other __ARGS((tabpage_T *tp, int forceit));
+void ex_all __ARGS((exarg_T *eap));
+void handle_drop __ARGS((int filec, char_u **filev, int split));
+void alist_clear __ARGS((alist_T *al));
+void alist_init __ARGS((alist_T *al));
+void alist_unlink __ARGS((alist_T *al));
+void alist_new __ARGS((void));
+void alist_expand __ARGS((int *fnum_list, int fnum_len));
+void alist_set __ARGS((alist_T *al, int count, char_u **files, int use_curbuf,
+                       int *fnum_list,
+                       int fnum_len));
+void alist_add __ARGS((alist_T *al, char_u *fname, int set_fnum));
+void alist_slash_adjust __ARGS((void));
+void ex_splitview __ARGS((exarg_T *eap));
+void tabpage_new __ARGS((void));
+void do_exedit __ARGS((exarg_T *eap, win_T *old_curwin));
+void free_cd_dir __ARGS((void));
+void post_chdir __ARGS((int local));
+void ex_cd __ARGS((exarg_T *eap));
+void do_sleep __ARGS((long msec));
+int vim_mkdir_emsg __ARGS((char_u *name, int prot));
+FILE *open_exfile __ARGS((char_u *fname, int forceit, char *mode));
+void update_topline_cursor __ARGS((void));
+void exec_normal_cmd __ARGS((char_u *cmd, int remap, int silent));
+int find_cmdline_var __ARGS((char_u *src, int *usedlen));
+char_u *eval_vars __ARGS((char_u *src, char_u *srcstart, int *usedlen,
+                          linenr_T *lnump, char_u **errormsg,
+                          int *escaped));
+char_u *expand_sfile __ARGS((char_u *arg));
+int put_eol __ARGS((FILE *fd));
+int put_line __ARGS((FILE *fd, char *s));
+void dialog_msg __ARGS((char_u *buff, char *format, char_u *fname));
+char_u *get_behave_arg __ARGS((expand_T *xp, int idx));
+/* vim: set ft=c : */
+#endif /* NEOVIM_EX_DOCMD_H */