Merge pull request #136 from forio/documentation

minor updates on documentation based on bug verification
Added facility to check if some functionality (a dependency) is included into the instance

For example line charts requires that cartesian is included in the instance
Added link to docs in missing dependency error
Added dependency check in all visualizations
moved local example loader script into index.js
Added a base rect to the plot area to have the ability to add a background color to the plot area that show behind the gridlines
Added note about background color to the documentation
pass 'last' data set to next visualization if no data was provided (chained data)
Enhanced tooltip with series name
Release 0.9.81
Fixed positioning of background rect
Release 0.9.82
Passed all overlapping points to the tooltip formatter function
Fixed tooltip marker expectation tests for line charts
Fixed test due to new background rect
Fixed test to account for half pixel fix
Fixed bar tests to account for new background rect and tooltip enable/disable functionality
Release 0.9.83
simplified style for axis ticks
Release 0.9.84