instead of global variables create context object and pass it as parameter

[Uzlopak]

Properly encapsulate the whole state of the builder. Preparation for further changes like implementing a possible strict mode as discussed in #579

Checklist

• run npm run test and npm run benchmark
• tests and/or benchmarks are included
• documentation is changed or added
• commit message and code follows the Developer's Certification of Origin
  and the Code of conduct

[Uzlopak]

I could have named it also state or so.

[mcollina]

lgtm