Added __slots__ for all classes (possible to reduce the memory)

[divaltor]

#36

I tried adding slots to classes to reduce memory consumption. Since when parsing real yml files it may contain several thousand offers and creating classes without slots may have a bad effect on memory

• All tests are passed

• No conflicts

• Tests on real file

The first image is a variant with slots, the second without them. I wouldn't say the difference is too big, but it's still a little better than nothing. The test may not be too plausible due to the fact that I additionally process it after it has loaded into memory and perhaps because of this, the difference is almost imperceptible. The test was performed on a 110 MB file

[codecov-commenter]

Codecov Report

Merging #37 into master will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master       #37   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           22        22           
  Lines         1147      1172   +25     
=========================================
+ Hits          1147      1172   +25     

Impacted Files	Coverage Δ
yandex_market_language/models/age.py	100.00% <100.00%> (ø)
yandex_market_language/models/category.py	100.00% <100.00%> (ø)
yandex_market_language/models/condition.py	100.00% <100.00%> (ø)
yandex_market_language/models/currency.py	100.00% <100.00%> (ø)
yandex_market_language/models/dimensions.py	100.00% <100.00%> (ø)
yandex_market_language/models/feed.py	100.00% <100.00%> (ø)
yandex_market_language/models/gift.py	100.00% <100.00%> (ø)
yandex_market_language/models/offers.py	100.00% <100.00%> (ø)
yandex_market_language/models/option.py	100.00% <100.00%> (ø)
yandex_market_language/models/parameter.py	100.00% <100.00%> (ø)
... and 3 more

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[stefanitsky]

@divaltor good job, but what about what we talked about earlier to use an iterator? Did you tried that? I think i can merge that, but i think this is not closes #36

[divaltor]

@stefanitsky I'm thinking how to do this so as not to break backward compatibility

[stefanitsky]

@stefanitsky I'm thinking how to do this so as not to break backward compatibility

Do you need to change models for this? If not, you can make another method and name it like iter_parse.