Fix unit tests
Update formatting behavior without exactdigits param

If $lengthint == 0 with $base of 2, 8, or 16: mask to 32 bits and display in as many digits as needed
If $base == 10: display in at least $lengthint digits before decimal point
Else: display in exactly as many digits as requested
Update formatting behavior: do not limit to 32 bits

If $lengthint == 0 with $base of 2, 8, or 16: mask to specified # of bits or do not mask at all
Update comments on acceptable bases
Remove old uses of $exactdigits
Fix format string difference from sprintf for decimal
Fix bug: remove trailing comma in calls
Group digits as requested
Update unit tests for formatting behavior changes
Update language for correct answer length behavior changes
Fix defaults for correctanswergroupdigits and exactdigits
Add correctanswershowbase option
Update exactdigits option in edit form
Add validation on correct answer lengths and exactdigits
Reduce maximum answer length to 64
Enforce maximum lengths in _format_in_base
Update edit form validation
Enforce exact number of digits if required
Fix typo in apply_units
Add missing $exactdigits to call to make_answer_processor