Add RenameKeywords transformer

[bhirsz]

Closes #183

[codecov-commenter]

Codecov Report

Merging #194 (ead89df) into main (d9a7cd6) will decrease coverage by 0.01%.
The diff coverage is 97.14%.

@@            Coverage Diff             @@
##             main     #194      +/-   ##
==========================================
- Coverage   97.32%   97.31%   -0.02%     
==========================================
  Files          26       27       +1     
  Lines        1458     1488      +30     
==========================================
+ Hits         1419     1448      +29     
- Misses         39       40       +1     

Impacted Files	Coverage Δ
robotidy/transformers/__init__.py	100.00% <ø> (ø)
robotidy/transformers/RenameKeywords.py	96.87% <96.87%> (ø)
robotidy/decorators.py	100.00% <100.00%> (ø)
robotidy/transformers/RenameTestCases.py	100.00% <100.00%> (ø)

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