Checking for SSL fault on connection

If the server on the endpoint does not support SSL correctly, a response.client object may not be available. Check before reading properties from response.client.
Added dependency badge for README file;

I would like to add VersionEye dependency badge, which shows a current state of dependencies and when user clicks on badge, then he/she will see an additional metadata, that doesnt exists on npmjs page, for example previous versions, release cycle and  sub-dependencies.
Added support for HTTP_PROXY and HTTPS_PROXY environment variables, if the proxy option isn't already set.
Won't use HTTP(S)_PROXY env var if proxy explicitly set to null.
Fix typo in form example
Documented tough-cookie installation.
failing test
extend passed in options
Merge pull request #891 from lalitkapoor/857-Options-object-is-mutated-by-calling-request

fixes 857 - options object is mutated by calling request
merge options
tilde?
Merge pull request #897 from vohof/patch/01

merge with default options
Fixes #555
Merge pull request #901 from pigulla/master

Fixes #555
2.35.0
2.35.1
Reventing lodash merge change.
2.36.0
2.36.1
append secureOptions to poolKey