Add all tests provided by Professor
Run all tests if no command line arguments
Add file local variable cookie to run_test
Fix parser bug: scan '!=' operator
Fix infinite recursion bug in while loops

Certain nested loops would result in infinite recursion when trying to
replace variables that were assigned to in the loop body.
Output .svg images during testing

This is mostly so that the 'big' test doesn't fail since dot is unable
to make such a massive bitmap. The svg output can't be displayed for
big, but it will keep the test from failing.
Create svg images of reference outputs

This is to be comparable to the test script.
Ignore .svg files
Add command line options to run_test

If you pass a sequence of test names, only those tests will be ran, if
you pass the argument '-ref' the reference output will be created for
that test.
Only make the result directory if running tests
Add check for existence before opening in_file
Add test001 reference output