`urllib.parse.unquote_to_bytes` should have an "escape plus" option, just like `urllib.parse.unquote_plus` does. 

It's very necessary in some cases:

```
# Say I have a url string: 'a+%2b%c0'. 
# In Python2, I can parse it into b'a +\xc0' with urllib.unquote_plus.
# Note that the first "+" was escaped into space, and the second "+" was decoded from "%2b".
# But in Python3, this just can't be done, either with urllib.parse.unquote, urllib.par.unquote_plus or urllib.parse.unquote_to_bytes.
# This is the example:

>>> from urllib import parse
>>> s = 'a+%2b%c0'
>>> parse.unquote(s)
'a++�'
>>> parse.unquote_plus(s)
'a +�'
>>> parse.unquote_to_bytes(s)
b'a++\xc0'
```

PS: the character "�" should be "À", but it can't be shown in command line.

The result of `urllib.parse.unquote_to_bytes` is almost what I want, except that it doesn't escape the first "+" into space.