Merge pull request #19 from mrbar42/webpack4-plugin-fix

explicitly check webpack version major, add plugin tests

Merge pull request #18 from mrbar42/fix-legacy-support

separate webpack 4 and 5 support, unify tests version enforcement

Merge pull request #16 from mrbar42/support-webpack-5

Support Webpack 5

Merge pull request #15 from mrbar42/update-deps

update dev deps, improve README

fix npmignore

Merge pull request #6 from mrbar42/support-all-webpack-versions

support both webpack 3 and 4

ignore tests folder, add npmignore