updated load-stuff to take an array from application.appNpmTasks for extra task loading.
added documentation on custom tasks
Merge branch 'load_appnpmtasks' of git://github.com/lygaret/lineman into lygaret-load_appnpmtasks
Renamed the configuration to loadNpmTasks

"app" isn't especially meaningful in this case, so
keeping the name the same as the grunt API seems
better to me (informed by my own messing up twice, 
thinking that the name was "addNpmTasks")
massaged the documentation around custom tasks