ConstantLine support

[dorroddorrod]

Hi,
Today we are using carbonapi and all his rendering features include constantLine:

We would like to use this project to render promethous metrics graph that looks the same as carbonapi but were missing the constantLine feature.
Are you planning to add it ?
Another question,
When rendering a prom metric with more tags than the page width its just cut off and not opening a new line.
There is a way to fix it ?