Move ast_printer into a debug/ folder.
Fix unit testing mode in script/debug.
Shift commandline arguments around.

--debug now activates debugging output for an individual phase (individually)
and --phase controls how far execution progresses. Change the unit testing
scripts and script/debug to use the new arguments to, for example, not invoke
the parser when testing the lexer.
Add an option to dump the symbol table, too.
Merge pull request #8 from smashwilson/flexible-debug

More flexible command line arguments