Adding support for dc.lineChart.curve. Deprecating interpolate/tension.

[kum-deepak]

Resolves #1376

Updated documentation and code examples. Looking forward to your feedback.

[gordonwoodhull]

Please add a warning here if _tension was specified but the curve doesn't support it.

[kum-deepak]

While fixing also realized that 0 is a valid value for _tension, which would have gotten discarded.

[gordonwoodhull]

This is really solid, careful work. Just one more backward-compatibility warning would help, I think.

Thank you for all your efforts.

[kum-deepak]

Thanks @gordonwoodhull, will add the warning soon. Currently deep into the zoom behavior.

[gordonwoodhull]

Thanks @kum-deepak! Made some tweaks and merged.

[kum-deepak]

Thanks @gordonwoodhull, all your changes make sense!

Any suggestions what I should pick up next?

[gordonwoodhull]

Thanks @kum-deepak, please review your comments and Upgrade Notes from #1363 and see if there is anything else you want to address.

After that, please start looking at the 4 PRs I listed there, which I believe are ready to go, but need to be ported to d3v4. I have not thoroughly reviewed them, so if you see anything that needs improvement, go for it. I think they are ready because they have passing automated tests and most of them have also been tested by people beside the author.

I will look at the transition issues and d3.stack. Apart from an issue or two in the examples, I think these are the only blockers for releasing a beta.

Congratulations, and thank you!