Add HTML source support

[klaasnicolaas]

This PR will do:

• ✨ Add support for Inverters with a HTML source
• 🧪 Add extra test or update for the new code
• 📚 Update the documentation
• 🔨 Use variables in the regex function

[codecov]

Codecov Report

Merging #38 (37f53ed) into master (8c6a10c) will increase coverage by 3.51%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #38      +/-   ##
==========================================
+ Coverage   91.42%   94.94%   +3.51%     
==========================================
  Files           4        4              
  Lines         140      178      +38     
  Branches       21       29       +8     
==========================================
+ Hits          128      169      +41     
+ Misses          9        7       -2     
+ Partials        3        2       -1     

Impacted Files	Coverage Δ
omnikinverter/exceptions.py	100.00% <100.00%> (ø)
omnikinverter/models.py	100.00% <100.00%> (ø)
omnikinverter/omnikinverter.py	86.95% <100.00%> (+8.00%)	⬆️

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