Trying to use CPS transform (WIP)
Implemented continuation-passing style interpreter
Not creating procs in initialisation
Updated 'is_f' for CPS

Updated 'is_f' for continuation passing style.
Working on CPS-interpreter
Problem with running Y-combinator
Changed eval_env and write_expression.
Starting over with smaller interpreter
Started using loop
Only calls are recursive now
Added some documentation
Got continuation-passing-style interpreter working
Added better test for continuation
Added handling of call with continuation
Added integers back
Added memoization and input
Updated TODO
Added strings and output
Added some assertions
Removing bison/flex files