Support for overriding column length

[tom-walford]

Hey,

I've run into an issue where a tool that uses the output of this plugin was failing to parse the tree structure due to truncation of the ascii graph. Sadly I was unable to change the size of the terminal (which is what determines the max column length when rendering the graph, and hence the trunking).

In SBT 1.0.2+ a setting was added - asciiGraphWidth that was intended to support setting the render width for ascii graphs - overriding the default behaviour in SBT of using terminal width. It would be great if the dependencyGraph plugin could also support this setting.