[#116] handle negative values in bar chart
[#116] improve y min/max value handling
improve negative value handling in stackable chart
[#116] implement negative elastic Y handling
[#116] improve bar chart test cases for handling negative values
[#116] improve bar chart handling of mixed positive and negative values
[#116] improve line chart handling of mixed positive and negative values
[#116] implement line chart handling of mixed positive and negative values with stacking
Extract method refactor of onClick

The implementation of the two portions of the `if` statement were the
same.  This pulls that into a common function that can be used directly
to in case someone needs to programmatically set the filter values.

Note, `onClick` did not have any direct tests, so I wasn't sure how I
should proceed with that.  All current tests still pass, so assuming
they have adequate indirect coverage of `onClick`, this should be ok.
improve onClick test coverage
Merge pull request #122 from tswicegood/extract-onClick-implementation

Extract method refactor of onClick
Merge branch 'master' of github.com:NickQiZhu/dc.js
improve onClick test coverage
upgrade d3 to v3 and fix some broken test cases
upgrade d3 from v2 to v3
fix pie chart test cases
[#106] upgrade d3 to v3
fix npm dependency typo
Merge branch 'master' of github.com:NickQiZhu/dc.js
[#115] fix stackable chart dynamic accessor switch not working issue