* Add dual-axis line chart to viz
- Add a new viz using two y axis for multi-chart in nvd3
- Option to set metric and axis format for two y axis
* Resolve conflicts
* Fixed x axis and resized thumbnail
* Added example to __init__.py
* Change get_df to match with format
* Add NVD3's bullet chart.
* Add empty lines before nested function definitions.
* Add thumbnail for bullet chart.
* Add bullet chart to gallery.rst.
* Add "requiresTime: false", fix indentation.
* Avoid scaling bullet chart vertically.
* Use a default if no range is specified.
* Fix coloring of bullet chart.