Issue #62: Allow setting timeout on Client level and for selected endpoints

[DavidHuebner]

• New timeout parameter and Client level and for some selected endpoints: Specifying the timeout for a selected endpoint prevails over the Client level timeout
• No tests were added; tested timeout parameter manually with a real Heath Discovery instance
• Added documentation for Client constructor, fixed sphinx config (removed specification for classes that do not exist anymore, __init__ is documented only for Client)
• Fixed copyright year

[codecov-commenter]

Codecov Report

Merging #77 (bf2bdb5) into dev (7647b5c) will decrease coverage by 0.13%. The diff coverage is 66.66%.

@@            Coverage Diff             @@
##              dev      #77      +/-   ##
==========================================
- Coverage   90.70%   90.56%   -0.14%     
==========================================
  Files          16       16              
  Lines        1678     1686       +8     
==========================================
+ Hits         1522     1527       +5     
- Misses        156      159       +3     

Impacted Files	Coverage Δ
averbis/core/_rest_client.py	84.42% <66.66%> (-0.22%)	:arrow_down:

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