Improve message spans in TypeCheck

Fixes #93 (closed)

This branch improves the messages from the TypeCheck by always using the span from the innermost expression in which the type error occurred.

Consider the example from the issue that now emits the following error message:

1:8-1:24 Error:
    Type error in application
    not (f True True)
     
    Term: (f True True)
    Inferred type: [Prelude.Char]
    Expected type: Prelude.Bool
    Types Prelude.Bool and [Prelude.Char] are incompatible
   | 
 1 | test = not (f True True)
   |        ^^^^^^^^^^^^^^^^^

Nested expressions now also yield a better span:

test = 23 + (3 * True) / 4

1:14-1:21 Error:
    Missing instance for Prelude.Num Prelude.Bool
    in infix application
    3 * True
     
    Term: True
   | 
 1 | test = 23 + (3 * True) / 4
   |              ^^^^^^^^