Add automatic check for server version when instantiating client

[bachya]

Describe what the PR does:

linkding recently released a version that adds a /health API endpoint (sissbruecker/linkding#392). This allows us to ensure this library complies with a minimum required linkding version.

The breaking change is because the client instantiation process has changed—we now do the following:

from aiolinkding import async_get_client

client = await async_get_client(...)

...instead of:

from aiolinkding import Client

client = await Client(...)

A few notes:

• We technically still support the old method of instantiating the object directly, so this isn't an actual breaking change. I'm merely marking it as such because I want people to see the release notes and use the new method.
• We only check the server version when instantiating the client; I don't currently see the need for checking before every API request.

Does this fix a specific issue?

N/A

Checklist:

• Confirm that one or more new tests are written for the new functionality.
• Run tests and ensure everything passes (with 100% test coverage).
• Update README.md with any new documentation.

[codecov]

Codecov Report

Merging #51 (b1aac8f) into dev (e720263) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##               dev       #51   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            7         7           
  Lines          103       123   +20     
=========================================
+ Hits           103       123   +20     

Impacted Files	Coverage Δ
aiolinkding/__init__.py	100.00% <100.00%> (ø)
aiolinkding/client.py	100.00% <100.00%> (ø)
aiolinkding/errors.py	100.00% <100.00%> (ø)

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[codeclimate]

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