Updating to httpclient 4.3

Removing deprecated classes and following new 4.3 builder creation pattern.
Updating docs
Merge pull request #555 from Banno/upgrade-httpclient-4.3

Updating to httpclient 4.3

Closes #538
Upgrade slf4j to version 1.7.6

http://www.slf4j.org/news.html
Merge pull request #556 from jsyrjala/slf4j-1.7.6

Upgrade slf4j to version 1.7.6