Added a :kind command to display kinds of types and type constructors.
Originally implemented by @eed3si9n here: https://gist.github.com/eed3si9n/3610635
Got helped by @xeno-by here: https://groups.google.com/forum/?fromgroups=#!topic/scala-internals/DdSg-qxOvyo
and @retronym here: http://stackoverflow.com/questions/15678616/getting-type-information-inside-scala-repl-via-imain