TODO list:

Critical:

- add float/double support (should be as small as possible while being
  usable for RISC code generator too).
- 0 is pointer - fix type compare
- add message if external function or variable not found.
- To check: 'sizeof' may not work if too complex expression is given.
- fix 'char' and 'short' casts (in function parameters and in assignment).
- function pointers to forward reference (patch code generator).

Not critical:

- fix multiple compound literals inits in blocks (ISOC99 normative
  example - only relevant when using gotos! -> must add boolean
  variable to tell if compound literal was already initialized).
- fix L"\x1234" wide string case (need to store them as ints ?) */
- fix preprocessor symbol redefinition
- better constant opt (&&, ||, ?:)
- add ELF executable and shared library output option (would be needed
  for completness!).
- add PowerPC code generator.
- add portable byte code generator and interpreter for other
  unsupported architectures.