macro expansion: Fixed bug that prevented nested macros from expanding

macro expansion: Fixed bug that prevented nested macros from expanding
correctly.

The way nested macros were handeled previously was broken in many ways.
Now we tokenize the first expansion's lines and expand them
individually.
This fixed nested macros.
Previosuly it was also possible to get stuck in an infinite loop.

The current implementation uses a lot of ulas_str and malloc/free which
is not great, but in the end it should be ok.