Add strict mode to check for malformed headers (long strings)

[mnapoli]

No description provided.

[rcambien]

Thank @mnapoli !

Reading the report I thought the strict mode will focus on the wrong number of newlines but your solution is simpler to detect malformed headers.

I suggest to move the length check directly in the constructor to avoid loading data in memory sooner.

I also check my use cases and I think it's safe to set an hard limit without the strict flag. From what I read, most web server allow a maximum of 8192 characters for an header line, it seem to be a good value for all commun use cases and it will fix the original problem.

Can you update the PR ?

[mnapoli]

@rcambien thanks, done!