Merge branch 'add-pseudoplain-tests' into 'master'

__tests__/pseudoplain-gmail-gmail.test.ts

__tests__/pseudoplain-gmail-outlook.test.ts

__tests__/pseudoplain-outlook-outlook.test.ts

__tests__/utils.ts

dist/HTMLNormalizer/HTMLNormalizer.d.ts

dist/HTMLNormalizer/HTMLNormalizer.js

dist/HTMLNormalizer/index.d.ts

dist/HTMLNormalizer/index.js

dist/PlainNormalizer/PlainNormalizer.js

dist/utils.js

package.json

src/HTMLNormalizer/HTMLNormalizer.ts

src/HTMLNormalizer/index.ts

src/PlainNormalizer/PlainNormalizer.ts

src/utils.ts