Implement get_ebp().

This will be used for doing backtraces.

This change adds the -fno-omit-frame-pointer compiler flag, so that the base pointer register always has a useful value.
Implement print_backtrace().

The print_backtrace() procedure does not yet look at debug info.  It ignoranly prints the Return Pointer and the first arguments in hex (brazenly assuming that these arguments exist!).
Implement demo_backtrace.
Merge pull request #2 from jasonpr59/backtrace

Implement print_backtrace().