introduce headerSize limit

[Uzlopak]

According to the comments, the maxHeaderSize should be actually be corresponding to the node http modules maxHeaderSize value. But it is actually wrong, as the default maxHeaderSize is and was always 8 kb and not 80 kb. On the other hand, the header of a request is different than the header of a multipart.

With this PR we expose headerSize as configurable limit. So if somebody wants to reduce the allowed size of a header, it is now possible to set the limit.

This PR is non-breaking, as the original 80 kbytes are still enforced. Maybe we should inform in a security part of the readme.md that we recommend to reduce the header size to something smaller.

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

[kibertoad]

We probably should mention these params in readme

[Uzlopak]

@kibertoad
They are in the section of limits. Or do you mean something else?

[kibertoad]

missed it, sorry

[Uzlopak]

@kibertoad
💯 % test coverage of headerparser.js

[kibertoad]

Woohoo!