Add kludgy way to restore privileged files (#58)

Author: ChanceNCounter

README.md

@@ -32,6 +32,8 @@ Don't worry, they're easy to remember after a minute:
 
 All of **bak**'s commands will disambiguate between multiple copies of the same file. In other words, you can `bak my_thing.txt` as many times as you want, until you're finished working, if you'd prefer to keep multiples instead of using `bak up`. At the moment, all you've got to go by are timestamps when it asks you to pick a .bakfile, but this will improve.
 
+**NOTE:** `bak down` will fall back on `sudo cp` if necessary. Please don't run `sudo bak`. This may create parallel config and bakfiles in root's XDG directories.
+
 ## Additional commands and flags
 
 `bak down --keep my_file` - Restores from .bakfile, does not delete .bakfile  

bak/commands/__init__.py

@@ -225,6 +225,10 @@ def bak_up_cmd(filename: Path):
     db_handler.update_bakfile_entry(old_bakfile)
     return True
 
+def _sudo_bak_down_helper(src, dest):
+    # TODO spin this off into a separate exec for sanity
+    click.echo(f"The destination {dest} is privileged. Falling back on 'sudo cp'")
+    call(f"sudo cp {src} {dest}".split(" "))
 
 def bak_down_cmd(filename: Path,
                  destination: Optional[Path],
@@ -270,7 +274,11 @@ def bak_down_cmd(filename: Path,
     if not confirm:
         console.print("Cancelled.")
         return
-    copy2(bakfile_entry.bakfile_loc, destination)
+    
+    try:
+        copy2(bakfile_entry.bakfile_loc, destination)
+    except PermissionError:
+        _sudo_bak_down_helper(bakfile_entry.bakfile_loc, destination)
     if not keep_bakfile:
         for entry in bakfile_entries:
             Path(entry.bakfile_loc).unlink(missing_ok=True)