Fix typos, spelling, grammar, etc

[jeffwidman]

Some quick docs cleanup

[codecov]

Codecov Report

Merging #545 into master will decrease coverage by 0.09%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master     #545     +/-   ##
=========================================
- Coverage   98.42%   98.32%   -0.1%     
=========================================
  Files          31       31             
  Lines        5017     5017             
=========================================
- Hits         4938     4933      -5     
- Misses         79       84      +5

Impacted Files	Coverage Δ
aiokafka/conn.py	98.82% <0%> (-0.89%)	⬇️
aiokafka/producer/producer.py	98.97% <0%> (-0.52%)	⬇️
aiokafka/consumer/consumer.py	98.46% <0%> (-0.31%)	⬇️

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[tvoinarovskyi]

Thanks!