Add suport for CURLINFO_CERTINFO and CURLOPT_CERTINFO.

This patch adds support for CURLINFO_CERTINFO (and CURLOPT_CERTINFO),
as well as documentation for them and a couple of minor documentation fixes.
These options appeared in libcurl 7.19.1.

The format of the returned information was chosen to be reasonably close
to the underlying libcurl data structure, while also allowing a
Python programmer to pass the cerificate info to dict() in order to get
a more convenient representation.

https://sourceforge.net/p/pycurl/patches/14/
Conditional compilation for CERTINFO bits
Use an ordinary DECREF
SSL certinfo test using github
Self signed certificate for ssl tests
Support for testing against a local ssl server
Test against a local ssl server
Merge pull request #36 from p-push/certinfo

CERTINFO support