Added `NTLM.createType2Message()` for testing (client does not need it).
Improved internals of `NTLM.createType2Message()` a bit.
Added NTLM test for fake NTLM Proxy authentication.
Improved NTLM test for real proxy server authentication: now one can set NTLM_USER, NTLM_DOMAIN, NTLM_PASS and NTLM_PROXY variables before running test. This allows testing communication with real server without a need to modify `test-ntlm.js` file.