Fix/local variables

[frendsick]

Resolves #54

Fix recursion by using the return stack for local variables.

Functions perform the following procedure:

1. Push the return address to the return stack
2. Push parameters to the return stack
3. Run the function
4. At the end of the function, drop its parameters from the return stack
5. Pop the return address from the return stack
6. Return to the popped return address

Note: The torth.torth compiler version can correctly compile all other known Torth programs except for itself. For some reason, the compiler version compiled by itself cannot compile another program anymore, as some list reference is zeroed. It causes a segfault at the first step of compilation, which includes all of the included files from every file referenced. A new issue will be opened for that bug which needs more debugging. In any case, I decided to merge the current version because it seems to work in other occurrences. The original compiler could even have worked because of some bug fixed alongside recursion.