v0.4

• ADD: Convenience methods to show widget from various sources
• ADD: PyTrajTrajectory adaptor
• ADD: MDAnalysisTrajectory adaptor
• ADD: NGLWidget.add_representation() method
• ADD: append a "WebGL not supported message" to widget if so
• ADD: parameters widget property, passed to NGL stage object
• ADD: params property for Structure, dict passed to NGL
• CODE: be less noisy when importing nglview
• DOC: more usage examples, API description
• DOC: added CHANGELOG file
• BUILD: added example files in the package