using exit codes as return value for function cb_symref_set_symbol_from_table()
changed return value of codeblock_execute() to indicate failure
always checking return value of function cb_syntree_eval()
implemented unit-test for error messages and error checking
fixed potential memory-leaks
implemented symobl-destructors for bison in case of parsing errors
implemented unit-test for syntax errors
fixed concluding parser error messages
checking for errors when performing a function call
checking errors in builtin function Eval() (bif_eval)
fixed error message
declaring symbols with the same name is not allowed anymore
codeblock now can be executed one or more times
updated codeblock unit-test
fixed scope comparison
updated unit-tests for symtab and scope
fixed comment
removed unnecessary error message
added unit-tests for runtime errors
Refactoring: Renamed codeblock string constants