the first version that might actually work

handle strings, nested comments, add some missing tokens
cool has single line comments too -- who knew?
grading code
apparently the at sign (@) is used for something
updated grades
Fix newlines in strings
detect end-of-file
fix handling of errors in strings

continue parsing after the rest of the string instead of right away
restore handling of newlines in strings

it was right before.  for a newline in a string, resume parsing on the
next line, don't look for the end of the string
passes all tests

this version passes all tests, but it's still not exactly the same as the reflexer
add null_in_string_escaped_newline -- my lexer differs from reflexer on this
Change the way we handle string escaping and errors.

Instead of a separate lex state, just use boolean sentinels.
This seems to be more consistent with the reflexer
prepare the directory for assignment 2 (PA3)