Improved function table functions radically

At this point, a rather good-looking function table can be printed with
this call and looks like the below shown table:

ghci> defaultFunctionTable 0 40 10 (Fraction 1 (Variable 'x'))
              x       (1.0 / x)
--------------- ---------------
         0.0000        Infinity
        10.0000          0.1000
        20.0000          0.0500
        30.0000          0.0333
        40.0000          0.0250

We're also not using any third-party packages anymore for
pretty-printing but the standard Text.PrettyPrint.