Show type information

[ochrons]

Add functionality to show the type information for a selected expression.

ref: https://github.com/scala/scala/blob/4c2c4c17bedb0627f6caaa44b0ab4c58a8949b71/src/repl/scala/tools/nsc/interpreter/PresentationCompilation.scala#L95

[chaotic3quilibrium]

Adding types is a crucial feature for people brand new to Scala. They need to be able to make out the type the compiler inferred. Otherwise, all sorts of natural confusion occur due to the complexity of Scala's type system and accidental edge cases.