Stop compilation when an unexpected character is encountered.
Support for floating point literals.
Adding support for functions.
Emitting prototypes for all declared functions.
Documenting function declaration and invocation in README.
Allow floating point literals with exponent and without decimal part.
Enclose output expression in ().
Hello World

There cannot be any programming language without a Hello World.
Don't assume Italian accented characters are available.
Accept "supercazzora" as alternate spelling of "supercazzola".

As mentioned in #2
Void functions might not return a value.
Make in() static since it's not supposed to be used outside the lexer.
Crediting the people who contributed to the initial specs.
Accented letters vs. backtick + smal fix to README.
More meaningful example for bituma comment.
Show the variable name when asking the user for some input.
Add a note to Specification.txt to remark that it's not up-to-date.
Uniform token naming convention.
Getting rid of explicit stacks with more left-recursive rules.

As a result, the grammar should be more readable.
Removing extra \n when no functions are defined.