`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.

This issue still stands. The output of all three methods is exactly the same as it was when the original question was posted. Would it maybe make sense to add a flag to the unquote_to_bytes method to parse the 'plus' symbol as a space? Or maybe create a new method(i.e. unquote_to_bytes_plus)?

pinging the issue to try get the PR reviewed