chore: introduce build file
chore: introduce build file

Steps this file does:
- empty the build directory
- make sure folders needed exist
- alter and copy the package.json file
- copy the license file
- copy the readme file
- copy all sources, without the test sources. Run them through babel
with only plugins to ensure valid JS
- build esm package
- build minified esm package
- build umd package
- build minified umd package

itslanguage/itslanguage-js,itslanguage/itslanguage-js