sample2.dat: Virtual data for a second test grading.
sample1.dat: renamed sample.dat file to simulated more than one test to a given class.
grade.pl: It's now implemented using hashes (key is obviously student's
	  id) and now the program reader the optical reader file and
	  another file contained students grades in previous tests. Then
	  it includes the new grade for each student. It seems that all
	  that is missing is use this file to write HTML files with the
	  grades.
sample.dat: renamed to sample1.dat
.gitignore: added T*.dat (files containing students ids and their grades to ignorelist.
grade.pl, loa.pl, test_span.pl: Included consistency check (number of arguments) from the program call.
sample2.dat: Changed a few answers and misreadings from optical reader.
grade.pl: Seems to do the complete job now, that is, reads the optical
	  reader file from a class, searches for test kind of each
	  student, grade its test, appends the scores to the
	  corresponding class .dat file and, finally, uses it to create
	  an HTML file with students' scores.

	  It would be desirable, after at least three tests are done,
	  the program to append an extra column with the final score of
	  each student.