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/mark.h

@@ -0,0 +1,37 @@
+#ifndef NEOVIM_MARK_H
+#define NEOVIM_MARK_H
+/* mark.c */
+int setmark __ARGS((int c));
+int setmark_pos __ARGS((int c, pos_T *pos, int fnum));
+void setpcmark __ARGS((void));
+void checkpcmark __ARGS((void));
+pos_T *movemark __ARGS((int count));
+pos_T *movechangelist __ARGS((int count));
+pos_T *getmark_buf __ARGS((buf_T *buf, int c, int changefile));
+pos_T *getmark __ARGS((int c, int changefile));
+pos_T *getmark_buf_fnum __ARGS((buf_T *buf, int c, int changefile, int *fnum));
+pos_T *getnextmark __ARGS((pos_T *startpos, int dir, int begin_line));
+void fmarks_check_names __ARGS((buf_T *buf));
+int check_mark __ARGS((pos_T *pos));
+void clrallmarks __ARGS((buf_T *buf));
+char_u *fm_getname __ARGS((fmark_T *fmark, int lead_len));
+void do_marks __ARGS((exarg_T *eap));
+void ex_delmarks __ARGS((exarg_T *eap));
+void ex_jumps __ARGS((exarg_T *eap));
+void ex_changes __ARGS((exarg_T *eap));
+void mark_adjust __ARGS((linenr_T line1, linenr_T line2, long amount,
+                         long amount_after));
+void mark_col_adjust __ARGS((linenr_T lnum, colnr_T mincol, long lnum_amount,
+                             long col_amount));
+void copy_jumplist __ARGS((win_T *from, win_T *to));
+void free_jumplist __ARGS((win_T *wp));
+void set_last_cursor __ARGS((win_T *win));
+void free_all_marks __ARGS((void));
+int read_viminfo_filemark __ARGS((vir_T *virp, int force));
+void write_viminfo_filemarks __ARGS((FILE *fp));
+int removable __ARGS((char_u *name));
+int write_viminfo_marks __ARGS((FILE *fp_out));
+void copy_viminfo_marks __ARGS((vir_T *virp, FILE *fp_out, int count, int eof,
+                                int flags));
+/* vim: set ft=c : */
+#endif /* NEOVIM_MARK_H */