feat: remove cjs wrapper and generate types in commonjs format

[alexander-akait]

This PR contains a:

• bugfix
• new feature
• code refactor
• test update
• typo fix
• metadata update

Motivation / Use-Case

fixes #273, improve DX for types

Breaking Changes

Potentially yes, but we use babel and our code in commonjs format, so we should generate types in the same format

Additional Info

Now you can use:

import {Rule} from 'compression-webpack-plugin'

[codecov]

Codecov Report

Merging #277 (422ca3f) into master (d863988) will increase coverage by 0.19%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #277      +/-   ##
==========================================
+ Coverage   95.45%   95.65%   +0.19%     
==========================================
  Files           2        1       -1     
  Lines         110      115       +5     
  Branches       43       43              
==========================================
+ Hits          105      110       +5     
  Misses          5        5              

Impacted Files	Coverage Δ
src/index.js	95.65% <100.00%> (+0.23%)	⬆️

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