add first specific tests for all chart types (except for BoxPlot) and fix small issue with dot plot
add comment
add basic DataAdapter test
Merge branch 'master' into task/charts_base_tests
add convenience function docstring
fix python version compat issues...
fix small compat issues
add test (and quick fix) for TimeSeries chart
remove unused variables and debugging code
Merge pull request #1538 from bokeh/task/charts_base_tests

Add charts base tests