Raise WaybackError from URLError and include URL

[AntiCompositeNumber]

Changes

Traceback (most recent call last):
  File "/home/ac/git/waybackpy/waybackpy/wrapper.py", line 109, in get_response
    response = urlopen(req) #nosec
...
urllib.error.HTTPError: HTTP Error 404: NOT FOUND

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 2, in <module>
  File "/home/ac/git/waybackpy/waybackpy/wrapper.py", line 67, in save
    header = self.get_response(req).headers
  File "/home/ac/git/waybackpy/waybackpy/wrapper.py", line 111, in get_response
    raise WaybackError(e)
waybackpy.exceptions.WaybackError: HTTP Error 404: NOT FOUND

to

Traceback (most recent call last):
  File "/home/ac/git/waybackpy/waybackpy/wrapper.py", line 109, in get_response
    response = urlopen(req) #nosec
 ...
urllib.error.HTTPError: HTTP Error 404: NOT FOUND

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "<stdin>", line 2, in <module>
  File "/home/ac/git/waybackpy/waybackpy/wrapper.py", line 67, in save
    header = self.get_response(req).headers
  File "/home/ac/git/waybackpy/waybackpy/wrapper.py", line 111, in get_response
    raise WaybackError("Error while retrieving %s" % req.full_url) from e
waybackpy.exceptions.WaybackError: Error while retrieving https://web.archive.org/save/https://example.com

This provides more information (what URL caused the error) and accurately says that the exception in urlopen caused the WaybackError, not that they happened to both occur.

[codecov[bot]]

Codecov Report

Merging #19 into master will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #19   +/-   ##
=======================================
  Coverage   98.85%   98.85%           
=======================================
  Files           1        1           
  Lines          87       87           
=======================================
  Hits           86       86           
  Misses          1        1           

Impacted Files	Coverage Δ
tests/test_1.py	98.85% <0.00%> (ø)

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