add user agent header
tests for user agent header
0.5.0
use tilde instead of caret in npm dependencies to support older npm versions
test host header is su1.3scale.net
force newer npm version for all node versions
dropping compatibility with Node 0.6.x
Readme changes. Nodejs 0.6.x no longer supported
Merge pull request #16 from 3scale/add_client_header

Add client header