add Node.{info,exists,create,delete}
add Jenkins.xjobs and .jobnames
add _JenkinsObject base class
minor fixes

- s/print/print()/
- s/_url()/url()/
- s/_JenkinsObject/_JenkinsBase/
- s/base_url/baseurl/
make remotefs a required argument and factor out NodeLaunchMethod
convert to yield_fixture and abstract TempView
simplify reference testing api
add node tests
abstract config and config_etree properties
add node_info()
mention node methods in docs
bump version to 0.4.0