Connect related changes - add optional hooks

[RomanManz]

Commit b9ddce5 adding return value to connectReqHandler

• allows the connectReqHandler to return an error in order to interrupt requests when necessary
  Commit fff8ef1 adding optional connectRespHandler
• introduces optional support for a connectResponseHandler
• allows to interrupt a connection - our use case was to check for specific headers returned from the chained proxy
  Commit f0e6940 calling Hijack in handleHttps if defined
• adds hijack support to the connectMitm and connectHTTPMitm actions
• our use case was to inject additional headers in the connect responses when needed

[elazarl]

The use case is, you have a CA that singed another certificate once, and you want to use this certificate to sign websites, right?

Can you please add unit tests for the certificate functions?

[ErikPelli]

What is the purpose of this Pull Request? Can you explain the problem that you are trying to solve?