Code rearranged

Minor rearrangement of code for legibility
Evaluating call to function in environment

Evaluating call to very simple function in environment test passes
Evaluating direct call to lambda

Both tests for evaluating calling lambda directly pass
Evaluating non-function symbols

Evaluating symbols that are not a function test passes
Fixed error message for illegal closure call

Fixed error message for calling a closure with the wrong number of
arguments