recreator: added support for remarks

added function for rem command and rem operator codes; and added pointer
to this function to the table entries for these codes

added an is empty access function to recreator class to test if the
output string is empty (used for the rem operator code to determine if a
space should be added before the operator, which it should not do if at
the beginning of the line)

the expected recreated output files for translator test 15 (REM tests)
were updated to the expected recreated outputs, added an additional all
lower case rem statement (all statements are recreated correctly)