Library.formatList - only use the first line from metadata.summary

I'm using multilined and color'd summaries in my packages, using
`Meteor list` is formatting these and gives a strange result
https://github.com/raix/Meteor-CollectionFS/issues/79

This pr does
* Add the terminal width
* Only uses the first line of a package summery in the list

Should a summery pr. definition allways be one line or is multiline
summary allowed?
*If not I'm thinking if you would take a pr adding a `metadata.intro`/`description` or something that would be shown when adding packages to their projects instead?*