Reject programs with redundant data

[QGarchery]

The parser stops when it recognizes one program and discards the rest. For example when parsing the number 1 followed by the number 2 followed by the number 3, only the number 1 is taken into account:

Goal: return an error in case where more than one program is given as an input.
Hint: the token EOL can be used to mark the end of the input

[mlgarchery]

What is a program ? Is it one line ?
The front is now able to send a proper LaTeX document on multi lines (a Cell), should our compiler manage multilines ?

[QGarchery]

Our compiler manages multiple lines just fine, but not a full latex document yet. Let's keep it simple and use the input of katex as the standard.
What is sent to katex ?

[mlgarchery]

What is sent to the compiler is exactly what's in the textarea.
On the frontend it's rendered in a MathBlock for now