Add Consumer.exceptions property for handling client exceptions

[prkumar]

Fixes #57.

Each Consumer instance has an exceptions property that exposes an enum of standard HTTP client exceptions that can be handled:

try:
    repo = github.create_repo(name="myproject", auto_init=True)
except github.exceptions.ConnectionError:
    # Handle client socket error:
    ...

This approach to handling exceptions decouples your code from the backing HTTP client, improving code reuse and testability.

Here are the HTTP client exceptions that are exposed through this property:

• BaseClientException: Base exception for client connection errors.
• ConnectionError: A client socket error occurred.
• ConnectionTimeout: The request timed out while trying to connect to the remote server.
• ServerTimeout: The server did not send any data in the allotted amount of time.
• SSLError: An SSL error occurred.
• InvalidURL: URL used for fetching is malformed.

Of course, you can also explicitly catch a particular client error from the backing client (e.g., requests.FileModeWarning). This may be useful for handling exceptions that are not exposed through the Consumer.exceptions property, for example:

try:
    repo = github.create_repo(name="myproject", auto_init=True)
except aiohttp.ContentTypeError:
    ...

FYI: @daa

[codecov]

Codecov Report

Merging #117 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master   #117   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          25     25           
  Lines        1395   1410   +15     
  Branches      131    131           
=====================================
+ Hits         1395   1410   +15

Impacted Files	Coverage Δ
uplink/builder.py	100% <100%> (ø)	⬆️
uplink/clients/aiohttp_.py	100% <100%> (ø)	⬆️
uplink/clients/requests_.py	100% <100%> (ø)	⬆️
uplink/clients/exceptions.py	100% <100%> (ø)
uplink/exceptions.py

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